IRIS Nuggets
At least once a week a nugget by NASA's Interface Region Imaging Spectrograph (IRIS) is posted by one of the scientists operating the instrument.
[{"id":"pod_polito_vanessa_2024-04-04T19:00:51.663Z","submitter":"Soumya Roy","author":"Soumya Roy [1,2] and Durgesh Tripathi [1]","status":"published","creation-date":"2024-04-04T19:00:51.689Z","last-modified-date":"2024-04-12T04:52:10.45Z","credit":"[1] Inter-University Centre for Astronomy and Astrophysics, [2] Harvard-Smithsonian Center for Astrophysics","title":"Evolution of Mg II Intensities during Solar Flares","contentBlocks":[{"type":"text","text":"The%20Mg%20II%20k%20and%20h%20line%20intensity%20ratios%20can%20be%20used%20to%20probe%20the%20characteristics%20of%20the%20plasma%20in%20the%20solar%20atmosphere.%20In%20optically%20thin%20conditions%2C%20the%20intensity%20ratio%20of%20the%20k%20to%20h%20line%20is%202%3A1%20and%20lower%20when%20the%20medium%20is%20optically%20thick%20%28Kerr%20et%20al.%202015%3B%20Levens%20%26amp%3B%20Labrosse%202019%29.%20Here%2C%20we%20study%20the%20evolution%20of%20the%20intensities%20ratios%20of%20the%20Mg%20II%20h%20and%20k%20lines%20during%20the%20evolution%20of%20three%20flares%2C%20viz.%2C%20C-class%2C%20M-Class%2C%20and%20X-class.%20We%20focus%20on%20the%20dependence%20of%20line%20ratios%20on%20the%20underlying%20magnetic%20field%20strength."},{"type":"image","file":"","url":"nuggetvideos/2024/04/04/pod_polito_vanessa_2024-04-04T19%3A00%3A51.663Z/iris_nugget.png","hash":"cb06cd859e3ecf417e23fcfbd724383f","mimeType":"image/png","caption":"Figure%201.%20IRIS%20SJI%202796%20%26Aring%3B%20observation%20of%20the%204th%20November%202015%20flare.%20The%20filament%20material%20erupts%2C%20and%20the%20primary%20ribbons%20move%20through%20the%20IRIS%20raster%20FOV.%20The%20longer%20ribbon%20sweeps%20through%20the%20SJI%20field%20of%20view%20towards%20the%20north-east."},{"type":"text","text":"The%20NOAA%20AR%2012443%20produced%20a%20multiribbon%20GOES%20class%20M3.7%20flare%20on%20November%204%202015%20that%20began%20%7E%2013%3A31%20UT%20and%20peaked%20at%20%7E13%3A52%20UT.%20IRIS%20observed%20the%20flare%20with%20coarse%2016-step%20raster%20with%2050s%20raster%20cadence.%20The%20X%20and%20C%20class%20flares%20were%20observed%20with%20coarse%208-step%20and%20dense%2016-step%20rasters%20with%20131s%20and%2033s%20raster%20cadence%20respectively.%20We%20use%20AIA%201600%20%26Aring%3B%20and%20SJI%201400%20%26Aring%3B%20observations%20to%20align%20the%20IRIS%20raster%20to%20HMI%20observations%20and%20make%20the%20plate%20scales%20same.%20We%20then%20artificially%20raster%20the%20HMI%20observations%20%28Fig.%202%29."},{"type":"image","file":"","url":"nuggetvideos/2024/04/04/pod_polito_vanessa_2024-04-04T19%3A00%3A51.663Z/iris_nugget.001.jpeg","hash":"a2b753e7b47e5598e0ab2e2301a2bae5","mimeType":"image/jpeg","caption":"Figure%202.%20Integrated%20intensity%20maps%20in%20Mg%20II%20h%20%28panel%20a%29%20and%20k%20%28panel%20b%20%29%20line.%20The%20corresponding%20coaligned%20and%20artificially%20rastered%20HMI%20LOS%20magnetic%20field%20map.%20The%20magenta%20and%20lime%20green%20contours%20in%20panel%20%28c%29%20show%20the%20contours%20of%20Mg%20II%20h%20%28panel%20%28a%29%29%20and%20k%20%28panel%20%28b%29%29%20intensity."},{"type":"text","text":"To%20investigate%20the%20time%20evolution%20of%20the%20intensity%20ratio%20and%20its%20relationship%20with%20the%20photospheric%20magnetic%20field%2C%20if%20any%2C%20we%20binned%20the%20spectra%20from%20flaring%20pixels%20by%20their%20magnetic%20field%20strength.%20We%20fitted%20a%20double%20Gaussian%20profile%20with%20a%20constant%20background%20to%20both%20Mg%20II%20k%20and%20h%20lines%20separately%20%28Fig.%203%29.%20This%20is%20done%20to%20avoid%20the%20effects%20of%20the%20background%20and%20the%20possible%20contribution%20of%20any%20other%20spectral%20feature.%20We%20compute%20the%20line%20intensities%20by%20integrating%20the%20fitted%20Gaussian.%20We%20follow%20the%20same%20procedure%20for%20all%20flares."},{"type":"image","file":"","url":"nuggetvideos/2024/04/04/pod_polito_vanessa_2024-04-04T19%3A00%3A51.663Z/apjad2a46f7_hr.jpg","hash":"3adba44dc33b2ad60e01e291fed7b5d8","mimeType":"image/jpeg","caption":"Figure%203.%20Fitted%20line%20profiles%20for%20the%20binned%20spectra%20for%20various%20magnetic%20field%20strengths%20from%20various%20times."},{"type":"text","text":"For%20the%20M%20class%20flare%2C%20the%20intensity%20ratios%20rise%20sharply%20during%20the%20impulsive%20phase%2C%20from%20%7E1.20%20to%20%7E1.28%20right%20before%20the%20soft%20X-ray%20flux%20peaks%20as%20seen%20from%20GOES%20and%20decrease%20rapidly%20thereafter%20to%20lower%20than%20preflare%20values%20%7E1.12%20%28Fig.%204%29.%20The%20evolution%20of%20the%20Mg%20II%20line%20intensity%20ratios%20are%20also%20very%20similar%20for%20various%20strengths%20of%20magnetic%20flux%20densities.%20The%20Mg%20II%20k-to-h-line%20intensity%20ratio%20behaves%20similarly%20for%20the%20C-class%20flare.%20It%20peaks%20during%20the%20impulsive%20phase%20%28k%2Fh%20%7E%201.12%29%20and%20reduces%20to%20preflare%20values%20%28k%2Fh%20%7E%201.09%29%20during%20the%20decay%20phase%20of%20the%20flare.%20The%20change%20in%20Mg%20II%20k-to-h-line%20intensity%20ratio%20is%20less%20prominent%20for%20this%20flare%20than%20the%20M-class%20event.%20Unlike%20the%20M%20and%20C%20class%20flare%2C%20we%20do%20not%20find%20any%20detectable%20change%20in%20the%20intensity%20ratio%20during%20the%20flare.%20About%20two%20to%20three%20data%20points%20show%20an%20enhancement%20in%20the%20ratio%2C%20which%20is%20much%20before%20the%20start%20of%20the%20flare."},{"type":"image","file":"","url":"nuggetvideos/2024/04/04/pod_polito_vanessa_2024-04-04T19%3A00%3A51.663Z/iris_nugget_2.jpg","hash":"a020b6f8a290d562443e798cdeee8dea","mimeType":"image/jpeg","caption":"Figure%204.%20Time%20evolution%20of%20the%20Mg%20II%20k-to-h-line%20intensity%20ratio%20obtained%20from%20averaged%20spectrum%20over%20the%20corresponding%20magnetic%20flux%20bin%20as%20labelled%20for%20the%20M%20%284th%20November%202015%20in%20panel%20a%29%2C%20C%20%283rd%20February%202015%20in%20panel%20b%29%20and%20X%20%2822nd%20October%202014%20in%20panel%20c%29%20class%20flare%2C%20respectively.%20For%20better%20visibility%2C%20the%2020.9%20-%20184.4%20G%20and%20348.9%20-%20513.3%20G%20points%20are%20offset%20by%2030%20s%20and%20-30%20s%2C%20respectively%2C%20for%20the%20M%20class%20flare.%20The%20overplotted%20red%20solid%20line%20displays%20the%201-8%20%26Aring%3B%20GOES%20X-ray%20light%20curve."},{"type":"text","text":"Mg%20II%20profiles%20vary%20significantly%20in%20shape%20and%20spatially%20within%20the%20flaring%20region%20%28Panos%20et%20al.%202018%3B%20Sainz%20Dalda%20%26amp%3B%20De%20Pontieu%202023%29.%20We%20show%20that%20the%20Mg%20II%20k-to-h-line%20intensity%20ratios%20change%20during%20flares.%20For%20the%20M-class%20and%20C-class%20flares%2C%20the%20ratio%20increases%20at%20the%20start%20of%20the%20flare%2C%20peaks%20approximately%20halfway%20in%20the%20impulsive%20phase%2C%20and%20shows%20a%20steep%20decline%20thereafter.%20The%20ratios%20fall%20even%20below%20the%20preflare%20conditions%20during%20the%20later%20stage%20of%20the%20flare.%20However%2C%20this%20behaviour%20is%20only%20observed%20in%20the%20M-%20and%20C-class%20flares%20and%20not%20in%20the%20X-class%20flare.%0AOur%20observations%20showed%20no%20correlation%20between%20the%20line%20intensity%20ratios%20and%20magnetic%20flux%20density.%20The%20line%20intensity%20ratio%20for%20different%20magnetic%20field%20strengths%20similarly%20affects%20the%20Mg%20II%20k%20and%20h%20lines.%0AKerr%20et%20al.%20%282015%29%20studied%20Mg%20II%20k-to-h-line%20intensity%20ratios%20and%20their%20time%20variation%20for%20individual%20pixels%20in%20the%20quiet%20Sun%20region%20and%20flaring%20locations.%20While%20they%20found%20no%20change%20in%20the%20ratios%20for%20the%20quiet%20Sun%20region%2C%20they%20noted%20that%20flaring%20pixels%20did%20show%20variations%20in%20the%20intensity%20ratios.%20They%20speculated%20that%20this%20might%20be%20due%20to%20differences%20in%20heating%20conditions%20in%20the%20non-flaring%20and%20flaring%20atmospheres.%20However%2C%20they%20did%20not%20observe%20any%20correlated%20change%20in%20the%20ratio%20with%20respect%20to%20the%20flare%20light%20curve.%0AOur%20results%20align%20with%20those%20obtained%20by%20Kerr%20et%20al.%20%282015%29%2C%20where%20we%20also%20find%20that%20the%20change%20in%20the%20ratio%20is%20highest%20during%20the%20impulsive%20phase%20of%20the%20flare%20and%20starts%20to%20decrease%20before%20the%20flare%20reaches%20its%20maximum%20in%20GOES.%20Such%20changes%20may%20indicate%20variation%20in%20the%20opacity%20of%20the%20local%20medium.%20In%20this%20scenario%2C%20the%20optical%20depth%20first%20decreases%20during%20the%20impulsive%20heating%20phase%20and%20starts%20to%20increase%20during%20the%20decay%20phase.%20While%20the%20decrease%20in%20the%20optical%20depth%20during%20the%20impulsive%20phase%20may%20be%20attributed%20to%20localised%20heating%20and%20chromospheric%20evaporation%2C%20the%20increase%20during%20the%20decay%20phase%20of%20the%20flare%20may%20be%20explained%20by%20condensation%20and%20downflows."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2015A%26A...582A..50K/abstract\">Kerr, G. S., Simões, P. J. A., Qiu, J., & Fletcher, L. 2015, A&A, 582, A50</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019A%26A...625A..30L/abstract\">Levens, P. J., & Labrosse, N. 2019, A&A, 625, A30</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...861...62P/abstract\">Panos, B., Kleint, L., Huwyler, C., et al. 2018, ApJ, 861, 62</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023FrASS..1033429S/abstract\">Sainz Dalda, A., & De Pontieu, B. 2023, FrASS, 10, 1133429</a>","","","","","",""],"pubDate":"2024-04-12T16:20:41.211Z"},{"id":"pod_polito_vanessa_2024-03-05T19:00:56.574Z","submitter":"Seray Sahin","author":"Seray Sahin[1], Patrick Antolin[1], Clara Froment[2], Thomas A. Schad[3]","status":"published","creation-date":"2024-03-05T19:00:56.614Z","last-modified-date":"2024-03-09T10:23:17.603Z","credit":"[1] Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle Upon Tyne, NE1 8ST, UK, [2] LPC2E, CNRS/University of Orleans/CNES, 3A avenue de la Recherche Scientifique, Orleans, France, [3] National Solar Observatory, 22 Ohia Ku Street, Pukalani, HI 96768, USA","title":"Spatial and Temporal Analysis of Quiescent Coronal Rain over an Active Region","contentBlocks":[{"type":"text","text":"The%20solar%20corona%20contains%20cool%20and%20dense%20plasma%20structures%2C%20such%20as%20prominences%20and%20coronal%20rain%2C%20in%20addition%20to%20being%20hot%2C%20tenuous%2C%20and%20diffuse.%20Coronal%20rain%20is%20magnetized%20plasma%20that%20cools%20and%20condenses%20along%20coronal%20loops%2C%20producing%20spectacular%20showers%20of%20plasma%20that%20can%20be%20observed%20with%20high-resolution%20instruments.%20Coronal%20rain%20has%20been%20a%20subject%20in%20solar%20physics%20since%20the%201970s%20%28Leroy%201972%29%3B%20however%2C%20it%20has%20only%20been%20significantly%20studied%20in%20the%20last%20decade%20because%20it%20was%20considered%20simply%20downflows%20from%20prominence%20structures.%20Coronal%20rain%20is%20intimately%20linked%20to%20one%20of%20the%20most%20enduring%20mysteries%20in%20astrophysics%3A%20the%20coronal%20heating%20problem.%20%0A%0AThe%20prevailing%20hypothesis%20regarding%20coronal%20rain%20formation%20suggests%20that%20it%20arises%20from%20thermal%20instability%20%28TI%29%20within%20coronal%20loops%20in%20a%20state%20of%20thermal%20non-equilibrium%20%28TNE%29%2C%20referred%20to%20as%20the%20TNE-TI%20scenario%20%28Antolin%202020%29.%20In%20this%20scenario%2C%20radiative%20cooling%20locally%20overcomes%20the%20coronal%20heating%20input%2C%20resulting%20in%20regions%20of%20cool%20and%20dense%20condensations%20called%20rain%20clumps%2C%20which%20subsequently%20fall%20as%20coronal%20rain%20toward%20the%20solar%20surface%20under%20the%20action%20of%20various%20forces%20%28Oliver%20et%20al.%202014%29.%20In%20the%20presence%20of%20steady%20and%20strongly%20stratified%20heating%20%28Klimchuk%20%26amp%3B%20Luna%202019%29%2C%20TNE-TI%20undergoes%20repetitive%20cycles%2C%20resulting%20in%20long-period%20EUV%20intensity%20pulsations%20and%20periodic%20rain%20occurrences%20%28Froment%20et%20al.%202020%29.%20Coronal%20rain%20is%20mainly%20observed%20in%20quiescent%20and%20flaring%20active%20regions%20%28AR%29%2C%20and%20correspondingly%20referred%20as%20quiescent%20%28QSr%29%20or%20flare-driven%20%28FDr%29%20coronal%20rain.%20The%20QSr%20is%20the%20most%20common%20type%20of%20coronal%20rain%20associated%20with%20AR%20coronal%20loops.%20FDr%20coronal%20rain%20is%20observed%20during%20the%20cooling%20phase%20%28known%20as%20gradual%20phase%29%20of%20a%20solar%20flare.%0A%0AIn%20this%20study%20%28Sahin%20et%20al.%202023%29%2C%20we%20performed%20the%20first%20large-scale%20statistical%20investigation%20of%20QSr%20rain%20over%20an%20AR%20off-limb%20with%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%20and%20Solar%20Dynamics%20Observatory%20%28SDO%29%20instruments%20%28see%20Figure%201%29%2C%20spanning%20chromospheric%20to%20transition%20region%20%28TR%29%20temperatures.%20We%20focused%20on%20the%20origin%2C%20dynamics%2C%20and%20morphology%20of%20quiescent%20coronal%20rain%2C%20contributing%20to%20our%20understanding%20of%20coronal%20heating%20mechanisms."},{"type":"image","file":"","url":"nuggetvideos/2024/03/05/pod_polito_vanessa_2024-03-05T19%3A00%3A56.574Z/Figure1.png","hash":"541f88fd0106bcacaddfcf492c582380","mimeType":"image/png","caption":"Figure%201.%20The%20studied%20AR%20at%20the%20east%20limb%20of%20the%20Sun%20on%202017%20June%202%2C%20observed%20by%20IRIS%2FSJI%202796%20%26Aring%3B%20%28left%29%2C%20SJI%201400%20%26Aring%3B%20%28second%20from%20left%29%20and%2C%20SDO%2FAIA%20304%20%26Aring%3B%20%28third%20from%20left%29.%20The%20separated%20panel%20on%20the%20right%20shows%20a%20wider%20FOV%20with%20SDO%2FAIA%20171%20%26Aring%3B%20over%20the%20same%20AR%2C%20with%20the%20white%20rectangle%20outlining%20the%20FOV%20shown%20in%20the%20left%20panels.%20All%20images%20were%20obtained%20summing%20over%20ten%20images%20in%20the%20interval%2007%3A28%3A00%20%E2%80%93%2007%3A34%3A28%20UT.%20An%20animation%20of%20this%20figure%20is%20available%20in%20Sahin%20et%20al.%202023."},{"type":"text","text":"We%20detected%20coronal%20rain%20during%20the%205.45-hour%20observational%20time%20using%20the%20Rolling%20Hough%20Transform%20%28RHT%29%20technique%20developed%20by%20Schad%20%282017%29.%20Figure%202%20presents%20the%20average%20spatial%20%28rain%20inclination%29%20and%20temporal%20%28dynamical%20change%29%20mean%20angle%20maps%20of%20all%20detected%20rain%20pixels%20derived%20from%20RHT.%20We%20found%20that%20coronal%20rain%20is%20pervasive%20around%20the%20AR%20with%20similar%20quantities%2C%20morphologies%2C%20and%20dynamics%20throughout%2C%20suggesting%20that%20coronal%20heating%20operates%20in%20a%20similar%20manner%20over%20a%20very%20wide%20area%20around%20the%20sunspot.%20Sahin%20and%20Antolin%20%282022%29%20observed%20widespread%20rain%20showers%20over%20the%20same%20AR%20and%20estimated%20the%20TNE%20volume%20to%20be%20at%20least%2050%25%20of%20the%20AR%20volume%2C%20suggesting%20the%20prevalence%20of%20TNE%20over%20the%20AR.%20The%20finding%20also%20reveals%20that%20most%20of%20the%20coronal%20rain%20exhibits%20a%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href=\"https://ui.adsabs.harvard.edu/abs/2020PPCF...62a4016A/abstract\">Antolin, P., Plasma Phys. Control. Fusion 62(1), 014016 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...926L..29A/abstract\"> Antolin, P., Martinez-Sykora, J., and Sahin, S. ApJL 926(2), L29 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...633A..11F/abstract\">Froment, C., Antolin, P., Henriques, V. M. J., Kohutova, P. and Rouppe van der Voort, L. H. M. A&A 633, A11 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...884...68K/abstract\">Klimchuk, J.A. and Luna, M. ApJ 884(1), 68 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1972SoPh...25..413L/abstract\">Leroy, J.-L., SoPhys 25(2), 413-417 (1972)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...634A..36M/abstract\">Martinez-Gomez, D., Oliver, R., Khomenko, E., Collados, M. A&A 634, A36 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014ApJ...784...21O/abstract\">Oliver, R., Soler, R., Terradas, J., Zaqarashvili, T. V. and Khodachenko, M. L. ApJ 784, 21 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...931L..27S/abstract\">Sahin, S. and Antolin, P. ApJL 931(2), L27 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023ApJ...950..171S/abstract\">Sahin, S., Antolin, P., Froment, C. and Schad, T. A. ApJ 950(2), 171 (2023)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017SoPh..292..132S/abstract\">Schad, T., SoPhys 292(9), 132 (2017)</a>"],"pubDate":"2024-03-11T20:19:11.41Z"},{"id":"pod_polito_vanessa_2024-01-23T18:49:33.161Z","submitter":"Chris Nelson","author":"C. J. Nelson[1] , F. Auchere[2] , R. Aznar Cuadrado[3] , K. Barczynski[4,5], E. Buchlin[2] , L. Harra[5,4] , D. M. Long[6,7] , S. Parenti[2] , H. Peter[3], U. Schuhle[3] , C. Schwanitz[5,4], P. Smith[6] , L. Teriaca[3], C. Verbeeck[8] , A. N. Zhukov[8,9], and D. Berghmans[8]","status":"published","creation-date":"2024-01-23T18:49:33.192Z","last-modified-date":"2024-02-12T22:45:11.786Z","credit":"[1] European Space Agency (ESA), [2] Universite Paris-Saclay, [3] Max Planck Institute for Solar System Research, [4] ETH-Zurich, [5] Physikalisch-Meteorologisches Observatorium Davos, [6] UCL-Mullard Space Science Laboratory, [7] Queen's University Belfast, [8] Royal Observatory of Belgium, [9] Moscow State University","title":"Extreme-ultraviolet brightenings in the quiet Sun: Signatures in spectral and imaging data from the Interface Region Imaging Spectrograph","contentBlocks":[{"type":"text","text":"Small-scale%20brightenings%20are%20prevalent%20throughout%20the%20solar%20atmosphere%2C%20from%20Ellerman%20bombs%20%28Ellerman%2C%201917%29%20in%20the%20photosphere%20to%20EUV%20brightenings%20%28Berghmans%20et%20al.%2C%201998%29%20in%20the%20corona.%20These%20events%20are%20often%20hypothesized%20to%20be%20driven%20by%20the%20dynamic%20process%20known%20as%20magnetic%20reconnection%20%28Young%20et%20al.%202018%29%2C%20the%20instantaneous%20reconfiguration%20of%20the%20local%20magnetic%20field%20from%20a%20high-energy%20state%20to%20a%20lower%20energy%20state%2C%20meaning%20EUV%20brightenings%20could%20make%20a%20significant%20contribution%20to%20the%20energy%20budget%20of%20the%20upper%20solar%20atmosphere.%20The%20unparalleled%20spatial%20resolution%2C%20in%20terms%20of%20coronal%20imaging%2C%20obtained%20by%20the%20Extreme%20Ultraviolet%20Imager%E2%80%99s%20%28EUI%3B%20Rochus%20et%20al.%2C%202020%29%20High-Resolution%20Imager%20%28HRI%29%20on-board%20Solar%20Orbiter%20%28Muller%20et%20al.%2C%202020%29%20revealed%20for%20the%20first%20time%20that%20thousands%20of%20EUV%20brightenings%2C%20sometimes%20referred%20to%20as%20%E2%80%98campfires%E2%80%99%2C%20are%20present%20on%20sub-Mm%20scales%20throughout%20the%20quiet-Sun%20corona%20%28Berghmans%20et%20al.%2C%202021%29%2C%20potentially%20hinting%20that%20magnetic%20reconnection%20is%20more%20prevalent%20in%20the%20solar%20atmosphere%20than%20previously%20thought.%0A%0AOne%20of%20the%20key%20open%20questions%20regarding%20these%20small-scale%20EUV%20brightenings%20is%20whether%20they%20truly%20are%20signatures%20of%20dynamic%20heating%20to%20temperatures%20close%20to%201%20MK%2C%20or%20whether%20they%20have%20lower%20temperatures%20but%20somehow%20still%20exhibit%20a%20signature%20in%20the%20%28relatively%29%20broadband%20filter%20of%20the%20EUI%2FHRI%20instrument.%20To%20test%20this%2C%20one%20must%20use%20coordinated%20observations%20sampled%20by%20both%20EUI%2FHRI%20and%20other%20instruments%20to%20investigate%20the%20intensity%20evolutions%20of%20spectroscopic%20imaging%20data%20sampled%20at%20various%20temperatures.%20The%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%3B%20De%20Pontieu%20et%20al.%2C%202014%29%20has%20conducted%20numerous%20coordinated%20observations%20with%20the%20EUI%2FHRI%20instrument%20providing%20combined%20datasets%20with%20temperature%20coverage%20spanning%20around%200.01-1%20MK%20that%20are%20perfect%20for%20such%20analyses.%20One%20such%20dataset%20was%20sampled%20on%208%20March%202022%20and%20was%20used%20by%20Nelson%20et%20al.%20%282023%29%20to%20study%20the%20transition%20region%20response%20to%20the%20smallest%20scale%20EUV%20brightenings%20evident%20in%20EUI%2FHRI%20data.%20%0A%0AIn%20Fig.%201%2C%20we%20plot%20a%20region%20in%20the%20quiet-Sun%20around%20a%20grouping%20of%20EUV%20brightenings%20%28outlined%20by%20the%20aqua%20contours%29%20for%20the%20IRIS%20Mg%20II%20%28left%20panel%29%2C%20IRIS%20Si%20IV%20%28middle%20panel%29%2C%20and%20EUI%2FHRI%20174%20%26Aring%3B%20channel%20%28right%20panel%29.%20In%20this%20instance%2C%20a%20bright%20structure%20is%20immediately%20evident%20in%20the%20IRIS%20Si%20IV%20filter%2C%20co-spatial%20to%20the%20main%20body%20of%20the%20EUV%20brightening%20identified%20in%20the%20EUI%2FHRI%20image.%20No%20clear%20signature%20was%20present%20in%20the%20Mg%20II%20channel%20indicating%20that%20this%20event%20may%20have%20temperatures%20above%2020%20kK."},{"type":"image","file":"","url":"nuggetvideos/2024/01/23/pod_polito_vanessa_2024-01-23T18%3A49%3A33.161Z/Screenshot 2024-02-12 at 21.34.53.png","hash":"b604796d852ad6fa486787a5973057f7","mimeType":"image/png","caption":"Figure%201.%20%28Left%20panel%29%20A%20map%20of%20the%20Mg%20II%20SJI%20intensity%20around%20an%20EUV%20brightening%20that%20was%20identified%20in%20EUI%2FHRI%20data%20%28aqua%20contours%29.%20%28Middle%20panel%29%20The%20same%20field-of-view%20as%20sampled%20by%20the%20IRIS%20Si%20IV%20SJI%20filter.%20A%20clear%20brightening%20is%20evident%20co-spatial%20to%20the%20EUV%20brightening%20in%20the%20centre%20of%20the%20image.%20%28Right%20panel%29%20The%20EUV%20brighting%20as%20observed%20by%20the%20EUI%2FHRI%20instrument."},{"type":"text","text":"In%20Fig.%202%2C%20we%20plot%20another%20example%20of%20an%20EUV%20brightening%2C%20however%2C%20this%20time%20different%20behaviour%20is%20apparent.%20Once%20again%2C%20a%20bright%20structure%20is%20apparent%20in%20the%20EUI%2FHRI%20data%20%28right%20panel%29%2C%20but%20on%20this%20occasion%20no%20co-spatial%20or%20co-temporal%20brightening%20is%20apparent%20in%20either%20IRIS%20SJI%20channel.%20One%20potential%20explanation%20for%20this%20is%20that%20this%20EUV%20brightening%20is%2C%20indeed%2C%20formed%20at%20coronal%20temperatures%2C%20well%20above%20the%20temperature%20ranges%20sampled%20by%20either%20the%20Mg%20II%20or%20Si%20IV%20filters.%20Several%20examples%20such%20as%20this%20were%20present%20in%20the%20dataset%2C%20with%20typically%20smaller%20point-like%20EUV%20brightenings%20returning%20no%20signature%20in%20IRIS%20imaging%20data."},{"type":"image","file":"","url":"nuggetvideos/2024/01/23/pod_polito_vanessa_2024-01-23T18%3A49%3A33.161Z/Screenshot 2024-02-12 at 21.35.54.png","hash":"1ab8ed19f0eabec76a02faf438f43776","mimeType":"image/png","caption":"Figure%202.%20Same%20as%20for%20Fig.%201%2C%20but%20for%20an%20example%20EUV%20brightening%20where%20no%20co-spatial%20or%20co-temporal%20response%20was%20evident%20in%20the%20IRIS%20SJI%20data."},{"type":"text","text":"In%20order%20to%20investigate%20the%20thermal%20evolution%20of%20EUV%20brightenings%2C%20we%20constructed%20lightcurves%20for%20the%20IRIS%20Mg%20II%20SJI%20filter%2C%20IRIS%20Si%20IV%20SJI%20filter%2C%20and%20the%20EUI%2FHRI%20174%20%26Aring%3B%20data%20co-spatial%20to%20several%20events%20that%20were%20apparent%20in%20each%20of%20these%20channels.%20Four%20such%20lightcurve%20groups%20are%20plotted%20in%20Fig.%203%2C%20where%20varying%20behaviour%20is%20evident.%20In%20the%20left%20panel%2C%20the%20EUI%2FHRI%20intensity%20peaks%20before%20the%20IRIS%20filters%2C%20potentially%20indicating%20cooling%20of%20the%20local%20plasma.%20In%20the%20second%20panel%2C%20all%20three%20filters%20peak%20simultaneously%20potentially%20indicating%20either%20rapid%20heating%20or%20some%20form%20of%20catastrophic%20cooling.%20The%20right%20two%20panels%20both%20show%20examples%20where%20the%20IRIS%20intensities%20peak%20before%20the%20EUI%2FHRI%20intensities%2C%20potentially%20indicating%20heating.%20Overall%2C%20it%20is%20clear%20that%20all%20EUV%20brightenings%20do%20not%20follow%20the%20same%20thermal%20evolution%20meaning%20further%20research%20is%20required%20to%20fully%20understand%20them%20in%20the%20future."},{"type":"image","file":"","url":"nuggetvideos/2024/01/23/pod_polito_vanessa_2024-01-23T18%3A49%3A33.161Z/Screenshot 2024-02-12 at 21.35.03.png","hash":"1b1a0d350f2d711a3e2e32acc1b816af","mimeType":"image/png","caption":"Figure%203.%20Plots%20displaying%20the%20intensity%20evolutions%20of%20regions%20surrounding%20four%20individual%20EUV%20brightenings.%20Three%20different%20imaging%20filters%20are%20plotted%2C%20including%20the%20IRIS%20Mg%20II%20filter%20%28blue%20line%29%2C%20the%20IRIS%20Si%20IV%20filter%20%28red%20line%29%2C%20and%20the%20EUI%2FHRI%20174%20%26Aring%3B%20filter%20%28black%20line%29.%20Different%20behaviour%20is%20evident%20in%20each%20case%2C%20with%20intensity%20increases%20progressing%20from%20hotter%20to%20cooler%20channels%20%28left%20panel%29%2C%20intensities%20simultaneously%20increasing%20%28second%20panel%29%2C%20and%20intensity%20increases%20progressing%20from%20cooler%20to%20hotter%20channels%20%28right%20two%20panels%29%20all%20being%20evident."},{"type":"text","text":"To%20further%20analyse%20the%20transition%20region%20response%20to%20these%20events%2C%20we%20also%20investigated%20whether%20any%20EUV%20brightenings%20were%20sampled%20by%20the%20IRIS%20slit.%20Only%20one%20clear%20example%20was%20discovered%20in%20this%20short%20dataset%2C%20meaning%20general%20inferences%20cannot%20be%20made.%20However%2C%20this%20is%20a%20useful%20case%20study.%20In%20the%20left%20panels%20of%20Fig.%204%20we%20plot%20intensity%20maps%20sampled%20during%20one%20raster%20across%20this%20EUV%20brightening%2C%20where%20a%20clear%20elongated%20bright%20structure%20is%20evident%20in%20the%20transition%20region%20data.%20The%20right%20panels%20plot%20the%20spectra%20at%20either%20end%20of%20the%20structure%2C%20with%20bi-directional%20flows%20being%20immediately%20evident.%20The%20spectra%20measured%20at%20these%20locations%20are%20reminiscent%20of%20%E2%80%98explosive%20events%E2%80%99%20%28Brueckner%20%26amp%3B%20Bartoe%2C%201983%29%2C%20which%20are%20thought%20to%20be%20formed%20by%20magnetic%20reconnection%20in%20low-lying%20loops%20in%20the%20solar%20atmosphere."},{"type":"image","file":"","url":"nuggetvideos/2024/01/23/pod_polito_vanessa_2024-01-23T18%3A49%3A33.161Z/Screenshot 2024-02-12 at 21.36.31.png","hash":"97a74110523477a739aaf5037220cc6a","mimeType":"image/png","caption":"Figure%204.%20%28Left%20panels%29%20Intensity%20maps%20from%20four%20different%20spectral%20lines%20sampled%20across%20an%20EUV%20brightening%20that%20occurred%20co-spatial%20to%20the%20IRIS%20slit.%20%28Right%20panels%29%20Spectra%20sampled%20at%20the%20locations%20of%20the%20coloured%20crosses%20over-laid%20on%20the%20left%20hand%20panels.%20Clear%20bi-directional%20flows%20are%20evident.%20The%20vertical%20dot-dashed%20lines%20book-end%20the%20spectra%20range%20that%20was%20summed%20to%20construct%20the%20maps%20on%20the%20left."},{"type":"text","text":"Our%20research%20indicated%20that%20there%20is%20no%20%E2%80%98typical%E2%80%99%20response%20of%20transition%20region%20lines%20to%20the%20smallest-scale%20EUV%20brightenings%20detected%20in%20EUI%2FHRI%20coronal%20imaging%20observations.%20Some%20features%20exhibited%20strong%20responses%20in%20the%20IRIS%20Si%20IV%20lines%2C%20whilst%20others%20displayed%20no%20signature%20at%20all.%20One%20EUV%20brightening%20that%20was%20sampled%20by%20the%20IRIS%20slit%20displayed%20evidence%20of%20explosive%20event%20spectra%20in%20the%20transition%20region.%20Additional%20research%20on%20the%20wealth%20of%20coordinated%20observations%20collected%20by%20IRIS%20during%20subsequent%20Solar%20Orbiter%20Remote%20Sensing%20Windows%20will%20shed%20more%20light%20on%20this%20in%20the%20near%20future."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1998A%26A...336.1039B/abstract\">Berghmans, D., et al., A&A 336, 1039 (1998)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...656L...4B/abstract\">Berghmans, D., et al., A&A 656, L4 (2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1983ApJ...272..329B/abstract\">Brueckner, G. E. & Bartoe, J. D. F., ApJ 272, 329 (1983)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu, B., et al., SoPhys 289, 2733 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1917ApJ....46..298E/abstract\">Ellerman, F., ApJ 46, 298 (1917)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...642A...1M/abstract\">Muller, D., A&A 642, A1 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023A%26A...676A..64N/abstract\">Nelson, C. J., et al., A&A 676, A64 (2023)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...642A...8R/abstract\">Rochus, P., et al., A&A 642, A8 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018SSRv..214..120Y/abstract\">Young, P., et al, SSR 214, 120 (2018)</a>",""],"pubDate":"2024-02-13T22:01:36.002Z"},{"id":"pod_polito_vanessa_2023-12-13T18:26:43.224Z","submitter":"Serena Maria Lezzi","author":"Serena M. Lezzi [1,2], Vincenzo Andretta [2], Mariarita Murabito [3,4] & Giulio Del Zanna [5]","status":"published","creation-date":"2023-12-13T18:26:43.227Z","last-modified-date":"2024-01-09T11:59:34.702Z","credit":"[1] University of Naples "Federico II", [2] INAF Astronomical Observatory of Capodimonte, [3] INAF Astronomical Observatory of Rome, [4] ASI Space Science Data Center, [5] DAMTP University of Cambridge","title":"Dark Halos around active regions in the solar atmosphere","contentBlocks":[{"type":"text","text":"Dark%20areas%20around%20active%20regions%20%28ARs%29%20were%20first%20observed%20in%20chromospheric%20lines%20more%20than%20a%20century%20ago.%20They%20are%20known%20as%20%E2%80%9Ccircumfacules%E2%80%9D%20%28Hale%20%26amp%3B%20Ellerman%201903%3B%20Deslanders%201930%29%20and%20were%20later%20associated%20with%20the%20H%CE%B1%20fibril%20vortex%20around%20ARs%20%28Bumba%20%26amp%3B%20Howard%201965%3B%20Rutten%202007%29.%20Nowadays%2C%20dark%20areas%20surrounding%20ARs%20are%20also%20observed%2C%20as%20noted%20by%20Andretta%20%26amp%3B%20Del%20Zanna%20%282014%29%2C%20in%20spectral%20lines%20emitted%20in%20the%20transition%20region%20%28TR%29%20and%20the%20low%20corona.%20For%20example%2C%20they%20are%20observed%20particularly%20well%20in%20the%20SDO%2FAIA%20171%20%26Aring%3B%20images%20%28Wang%20et%20al.%202011%3B%20Singh%20et%20al.%202021%29.%20%0AWe%20name%20these%20chromospheric%2C%20TR%20and%20low%20coronal%20dark%20regions%20%E2%80%9Cdark%20halos%E2%80%9D%20%28DHs%29.%20%0ATR%20and%20coronal%20DHs%20are%20poorly%20studied%20and%2C%20because%20their%20origin%20is%20still%20unknown%2C%20to%20date%20it%20is%20not%20clear%20if%20they%20are%20related%20to%20the%20chromospheric%20fibrillar%20ones.%20Furthermore%2C%20they%20are%20often%20mistaken%20for%20coronal%20holes%20%28CHs%29."},{"type":"text","text":"DHs%20are%20large-scale%20structures%2C%20and%20are%20therefore%20difficult%20to%20observe%20in%20their%20entirety%2C%20except%20with%20instruments%20such%20as%20SDO%2C%20which%2C%20however%2C%20have%20limited%20TR%20coverage.%20This%20is%20the%20main%20reason%20why%20these%20structures%20have%20not%20been%20studied%20in%20detail%2C%20and%20IRIS%20full-disk%20mosaics%20represent%20a%20unique%20resource%20to%20investigate%20them."},{"type":"text","text":"In%20this%20work%20we%20characterize%20the%20emission%20properties%20of%20a%20DH%20by%20combining%20chromospheric%2C%20TR%2C%20and%20coronal%20observations%20in%20order%20to%20provide%20observational%20constraints.%20We%20also%20aim%20to%20investigate%20the%20different%20properties%20of%20DHs%20and%20CHs%20in%20order%20to%20provide%20a%20quick-look%20recipe%20to%20distinguish%20them.%20%0AWe%20study%20the%20DH%20around%20NOAA%2012706%20and%20the%20southern%20CH%20that%20were%20both%20visible%20on%20the%20disk%20on%20April%2022%2C%202018%20by%20analyzing%20IRIS%20full-disk%20mosaics%2C%20SDO%2FAIA%20filtergrams%20and%20SDO%2FHMI%20magnetograms."},{"type":"image","file":"","url":"nuggetvideos/2023/12/13/pod_polito_vanessa_2023-12-13T18%3A26%3A43.224Z/first_figure.png","hash":"7b28592c1b9230c4f0b529a4170a9b72","mimeType":"image/png","caption":"Figure%201.%20IRIS%20Mg%20II%20%5Cbegin%7Bequation%7Dh_3%5Cend%7Bequation%7D%20full-disk%20mosaic%2C%20AIA%20171%20%26Aring%3B%20and%20193%20%26Aring%3B%20full-disk%20images%20showing%20the%20DH%20surrounding%20NOAA%2012706%20in%20the%20northern%20hemisphere%20on%20April%2022%2C%202018.%20The%20inner%20and%20outer%20fibrillar%20DH%20contours%20are%20shown%20in%20red%20and%20green%2C%20respectively%3B%20the%20QS%20box%2C%20the%20coronal%20DH%20and%20the%20southern%20CH%20contours%20are%20shown%20in%20white%2C%20violet%20and%20blue%2C%20respectively.%20Fibrillar%20DH%2C%20coronal%20DH%20and%20CH%20are%20delimited%20by%20three%20contours%20of%20slightly%20different%20extents%20which%20take%20into%20account%20the%20degree%20of%20arbitrariness%20in%20the%20definition%20of%20the%20regions%20of%20interest%20and%20which%20were%20used%20to%20determine%20the%20uncertainties%20in%20the%20ratios%20of%20Figure%203."},{"type":"text","text":"The%20starting%20point%20of%20the%20analysis%20is%20the%20annular%20region%2C%20the%20emission%20of%20which%20is%20reduced%20compared%20to%20the%20QS%2C%20seen%20by%20eye%20in%20the%20IRIS%20Mg%20II%20%5Cbegin%7Bequation%7Dh_3%5Cend%7Bequation%7D%26amp%3B%5Cbegin%7Bequation%7Dk_3%5Cend%7Bequation%7D%20full-disk%20mosaics%2C%20where%20fibrils%20are%20clearly%20observed.%20We%20refer%20to%20this%20annular%20region%2C%20identified%20by%20the%20red%20and%20green%20contours%20in%20Figure%201%20and%20in%20Figure%202%20%28top%20left%20panel%29%2C%20as%20%E2%80%9Cchromospheric%20fibrillar%20DH%E2%80%9D.%0AIn%20the%20AIA%20171%20%26Aring%3B%20image%2C%20NOAA%2012706%20is%20surrounded%20by%20a%20spatially%20larger%20dark%20area%2C%20with%20coronal%20loops%20in%20the%20immediate%20vicinity%20of%20the%20AR%20core%20partially%20hiding%20the%20dark%20emission%20beneath%20them.%20We%20refer%20to%20this%20dark%20region%2C%20identified%20by%20the%20violet%20contour%20in%20Figure%201%2C%20as%20%E2%80%9Ccoronal%20DH%E2%80%9D.%20We%20also%20define%20a%20region%20of%20interest%20%28RoI%29%20for%20the%20southern%20CH%2C%20shown%20by%20the%20blue%20contour%20in%20Figure%201."},{"type":"image","file":"","url":"nuggetvideos/2023/12/13/pod_polito_vanessa_2023-12-13T18%3A26%3A43.224Z/Screenshot 2023-12-25 alle 19.16.11.png","hash":"6f7ce53d14e0d0f9e646314a5e1cf312","mimeType":"image/png","caption":"Figure%202.%20Closeup%20views%20of%20NOAA%2012706%20and%20its%20surroundings."},{"type":"text","text":"We%20evaluate%20the%20DH%20and%20the%20CH%20intensity%20ratios%2C%20defined%20as%20the%20average%20intensity%20inside%20the%20RoI%20respect%20to%20the%20QS%20%28identified%20by%20the%20white%20box%20in%20Figure%201%29.%20These%20ratios%2C%20shown%20in%20Figure%203%20%28left%20panel%29%20in%20green%20%28DH%29%20and%20blue%20%28CH%29%2C%20are%20obtained%20from%20the%20IRIS%20mosaics%20for%20the%20chromospheric%20fibrillar%20DH%20and%20from%20the%20seven%20AIA%20bands%20for%20the%20coronal%20DH.%20The%20ratios%20reflect%20the%20fact%20that%20the%20DH%20seen%20in%20the%20C%20II%20and%20Si%20IV%20lines%20coincides%20with%20the%20region%20covered%20by%20Mg%20II-core%20fibrils%2C%20although%20no%20clear%20fibrillar%20pattern%20could%20be%20detected%20in%20those%20lines%20%28Figure%202%29.%20On%20the%20other%20side%2C%20the%20coronal%20DH%20clearly%20seen%20in%20the%20AIA%20171%20%26Aring%3B%20appears%20as%20a%20distinct%20feature%20also%20in%20the%20304%20and%20131%20%26Aring%3B%20bands%20%28Figure%202%29.%0AFurthermore%2C%20the%20coronal%20DH%20and%20the%20CH%20show%20opposite%20AIA%20ratio%20behaviors%3A%20the%20former%20is%20indeed%20observed%20in%20the%20cooler%20AIA%20bands%20%28304%2C%20131%2C%20171%20%26Aring%3B%29%3B%20the%20latter%20is%20observed%20in%20all%20AIA%20bands%2C%20but%20it%20is%20darkest%20in%20the%20193%20and%20211%20%26Aring%3B.%20This%20trend%20is%20also%20confirmed%20by%20the%20coronal%20DH%20and%20CH%20emission%20measure%20%28EM%29%2C%20shown%20in%20the%20right%20panel%20of%20Figure%203."},{"type":"image","file":"","url":"nuggetvideos/2023/12/13/pod_polito_vanessa_2023-12-13T18%3A26%3A43.224Z/Screenshot 2023-12-25 alle 19.11.36.png","hash":"334e03e57d24d545e54d41ac6ded79d","mimeType":"image/png","caption":"Figure%203.%20Left%3A%20DH%20%28in%20green%29%20and%20southern%20CH%20%28in%20blue%29%20average%20intensity%20ratios%20in%20IRIS%20lines%20and%20AIA%20filters.%20The%20shaded%20areas%20are%20the%20ratio%20uncertainties.%20Right%3A%20Average%20logEM%20curves%20as%20functions%20of%20logT%20calculated%20over%20the%20QS%2C%20coronal%20DH%2C%20and%20southern%20CH.%20In%20the%205.7%E2%80%935.9%20logT%20range%20the%20DH%20and%20the%20CH%20show%20a%20similar%20EM%20depletion%20compared%20to%20the%20QS.%20At%20higher%20temperatures%20the%20CH%20exhibits%20a%20strong%20EM%20reduction%2C%20showing%20an%20opposite%20trend%20to%20that%20of%20the%20DH."},{"type":"text","text":"We%20also%20use%20a%2030-min%20sequence%20of%20HMI%20magnetograms%20to%20investigate%20the%20temporal%20evolution%20of%20the%20average%20signed%2C%20%26lt%3B%5Cbegin%7Bequation%7DB_%7BLOS%7D%5Cend%7Bequation%7D%26gt%3B%2C%20and%20unsigned%2C%20%26lt%3B%7C%5Cbegin%7Bequation%7DB_%7BLOS%7D%5Cend%7Bequation%7D%7C%26gt%3B%2C%20magnetic%20field%20strength%20inside%20the%20four%20RoIs.%20We%20find%20that%20both%20the%20fibrillar%20and%20the%20coronal%20DHs%20on%20average%20do%20not%20appear%20to%20be%20as%20markedly%20unipolar%20as%20the%20CH%20%28Figure%204%29."},{"type":"image","file":"","url":"nuggetvideos/2023/12/13/pod_polito_vanessa_2023-12-13T18%3A26%3A43.224Z/Screenshot 2024-01-09 alle 11.24.02.png","hash":"817cbe964374601e9da5effbcf633672","mimeType":"image/png","caption":"Figure%204.%2030-min%20time%20evolution%20of%20the%20average%20signed%20%28left%29%20and%20unsigned%20%28right%29%20magnetic%20field%20strength%20inside%20the%20four%20RoIs.%20The%20colored%20bands%20are%20the%20uncertainties."},{"type":"text","text":"To%20conclude%2C%20our%20analysis%20clearly%20shows%20that%20DHs%20and%20CHs%20exhibit%20different%20characteristics%2C%20and%20therefore%20should%20be%20considered%20as%20distinct%20types%20of%20structures%20on%20the%20Sun.%20We%20propose%20a%20simple%20recipe%20to%20distinguish%20between%20DHs%20and%20CHs%20that%20uses%20their%20different%20emission%20in%20the%20AIA%20filters%3A%20as%20illustrated%20by%20Figs.%201%20and%203%2C%20DHs%20are%20clearly%20outlined%20in%20the%20AIA%20171%20%26Aring%3B%20band%2C%20while%20they%20are%20nearly%20indistinguishable%20from%20quiescent%20coronal%20areas%20in%20the%20AIA%20193%20or%20211%20%26Aring%3B%20bands%3B%20on%20the%20contrary%2C%20CHs%20are%20dark%20in%20all%20AIA%20bands%2C%20but%20darkest%20in%20the%20193%20and%20211%20%26Aring%3B%20bands."},{"type":"text","text":""}],"references":["This article: <a href=\"https://ui.adsabs.harvard.edu/abs/2023A%26A...680A..61L/abstract\">Lezzi, S.M., Andretta, V., Murabito, M., Del Zanna, G. 2023, A&A 680, A61 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014A%26A...563A..26A/abstract\"> Andretta, V., & Del Zanna, G. 2014, A&A, 563, A26 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1965ApJ...141.1492B/abstract\">Bumba, V., & Howard, R. 1965, ApJ, 141, 1492 </a>","Deslanders, H. 1930, AnAPM, 4, 55","<a href=\"https://ui.adsabs.harvard.edu/abs/1903PYerO...3....1H/abstract\">Hale, G. E., & Ellerman, F. 1903, Publ. Yerkes Obs., 3, 3 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2007ASPC..368...27R/abstract\">Rutten, R. J. 2007, in The Physics of Chromospheric Plasmas, eds. P. Heinzel, I. Dorotovic, & R. J. Rutten (San Francisco, CA: ASP), ASP Conf. Ser., 368, 27</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021ApJ...909...57S/abstract\">Singh, T., Sterling, A. C., & Moore, R. L. 2021, ApJ, 909, 57 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2011ApJ...733...20W/abstract\">Wang, Y.-M., Robbrecht, E., & Muglach, K. 2011, ApJ, 733, 20 </a>","",""],"pubDate":"2024-01-10T16:12:31.303Z"},{"id":"pod_polito_vanessa_2023-12-02T00:55:35.896Z","submitter":"","author":"Pradeep Kayshap[1] & Peter R. Young [2,3]","status":"published","creation-date":"2023-12-02T00:55:35.934Z","last-modified-date":"2023-12-08T09:54:35.513Z","credit":"[1] VIT Bhopal University, India, [2] NASA Goddard Space Flight Center, USA, [3] Northumbria University, UK","title":"Center-to-limb variations in coronal hole and quiet Sun regions obtained with IRIS spectroscopic observations","contentBlocks":[{"type":"text","text":"Ultraviolet%20emission%20lines%20formed%20in%20the%20solar%20transition%20region%20%28TR%29%20at%20temperatures%20of%2010%3Csup%3E5%3C%2Fsup%3E%20K%20have%20long%20been%20known%20to%20exhibit%20Doppler%20redshifts%20and%20broadening%20in%20excess%20of%20the%20thermal%20broadening.%20Doschek%2C%20Feldman%20%26amp%3B%20Bohlin%20%281976%29%20were%20the%20first%20to%20report%20redshifts%20in%20TR%20lines%20from%20a%20study%20of%20Skylab%20S082-B%20spectra%2C%20finding%20Doppler%20shifts%20of%20up%20to%2015%E2%80%89km%E2%80%89s%3Csup%3E%E2%88%921%3C%2Fsup%3E.%20Enhanced%20non-thermal%20broadening%20at%20TR%20temperatures%20around%2010%3Csup%3E5%3C%2Fsup%3E%E2%80%89K%20was%20first%20reported%20by%20Boland%20et%20al.%20%281973%29.%20Both%20results%20likely%20give%20clues%20on%20the%20how%20mass%20and%20energy%20are%20balanced%20in%20the%20solar%20atmosphere.%20For%20example%2C%20non-thermal%20broadening%20may%20be%20caused%20by%20the%20passage%20of%20magnetohydrodynamic%20waves%20through%20the%20TR%2C%20while%20ubiquitous%20downflows%20in%20the%20TR%20represent%20mass%20and%20energy%20loss%20terms%20that%20need%20to%20be%20balanced%20to%20maintain%20a%20hot%20corona%20%28see%20Mariska%201992%2C%20for%20more%20details%29.%0A%0AOne%20method%20for%20characterizing%20the%20TR%20non-thermal%20broadening%20and%20Doppler%20shifts%20is%20to%20measure%20the%20emission%20line%20properties%20at%20different%20positions%20on%20the%20Sun%2C%20from%20the%20centre%20of%20the%20disc%20to%20the%20limb.%20Variations%20in%20the%20parameters%20then%20give%20clues%20as%20to%20the%20origin%20of%20the%20two%20effects.%20For%20example%2C%20if%20plasma%20flows%20are%20along%20radially%20aligned%20structures%20then%20net%20Doppler%20shifts%20would%20be%20expected%20to%20be%20at%20a%20maximum%20at%20disc%20centre%20and%20fall%20to%20zero%20at%20the%20limb.%20Similarly%2C%20if%20non-thermal%20broadening%20is%20due%20to%20random%2C%20lateral%20motions%20of%20radially%20aligned%20structures%2C%20then%20it%20would%20be%20expected%20to%20be%20largest%20at%20the%20limb%20and%20fall%20to%20zero%20at%20disc%20centre%20%28the%20motions%20giving%20a%20distribution%20of%20Doppler%20shifts%20when%20the%20line%20of%20sight%20is%20aligned%20to%20the%20motions%29.%0A%0AIn%20this%20work%2C%20we%20present%20the%20centre-to-limb%20variation%20%28CLV%29%20of%20the%20Doppler%20velocity%20and%20non-thermal%20broadening%20of%20the%20Si%E2%80%89IV%201402.77%E2%80%89%26Aring%3B%20TR%20emission%20line%20in%20both%20quiet%20Sun%20and%20coronal%20hole%20conditions%20across%20the%20full%20range%20of%20heliocentric%20angles.%20Although%20such%20a%20study%20has%20been%20performed%20for%20the%20quiet%20Sun%20previously%2C%20this%20work%20is%20the%20first%20for%20coronal%20holes.%20Si%E2%80%89IV%20is%20formed%20at%20around%2080%E2%80%89kK%20in%20the%20solar%20atmosphere%2C%20and%20the%20earlier%20work%20of%20Peter%20%26amp%3B%20Judge%20%281999%29%20suggests%20this%20line%20should%20show%20a%20redshift%20of%205%E2%80%938%20km%20s%3Csup%3E%E2%88%921%3C%2Fsup%3E%20at%20disc%20centre%20in%20the%20quiet%20Sun.%0A%0AThe%20IRIS%20full-disk%20mosaic%20dataset%20from%2024-25%20September%202017%20was%20chosen%20as%20the%20Sun%20exhibited%20a%20large%20low-latitude%20coronal%20hole%20in%20addition%20to%20the%20north%20pole.%20These%20are%20identified%20with%20white%20contours%20in%20Figure%201.%20Combined%2C%20the%20two%20coronal%20holes%20cover%20the%20complete%20range%20of%20heliocentric%20angles%2C%20%CE%B8%2C%20from%200%20to%2090%20degrees.%20Hence%20the%20dataset%20is%20ideal%20for%20measuring%20the%20CLV%20in%20coronal%20holes."},{"type":"image","file":"","url":"nuggetvideos/2023/12/02/pod_polito_vanessa_2023-12-02T00%3A55%3A35.896Z/figure1.png","hash":"4ecbbcccd53cad021eeba04408455240","mimeType":"image/png","caption":"Figure%201.%20The%20right%20panel%20shows%20the%20IRIS%20full-disc%20mosaic%20image%20from%20the%20Si%E2%80%89IV%201402.77%20%26Aring%3B%20line.%20The%20left%20panel%20shows%20a%20mosaic%20image%20constructed%20from%20AIA%20193%20%26Aring%3B%20images%20that%20were%20chosen%20to%20match%20the%20timing%20and%20pointing%20data%20from%20the%20IRIS%20mosaic.%20The%20QS%20region%20used%20for%20the%20CLV%20study%20is%20shown%20by%20a%20slanted%20blue%20patch%20that%20extends%20from%20the%20disc%20centre%20towards%20the%20south-west%20limb%20of%20the%20Sun.%20White%20contours%20denote%20the%20two%20CHs%20that%20were%20used%20for%20the%20CLV%20study."},{"type":"text","text":"The%20first%20step%20is%20to%20derive%20the%20CLV%20for%20the%20quiet%20Sun.%20The%20diagonal%20region%20%28blue%29%20on%20the%20images%20above%20was%20selected%2C%20and%20the%20Si%20IV%201402%20%26Aring%3B%20line%20was%20fit%20with%20a%20Gaussian%20function%20to%20yield%20integrated%20intensity%2C%20centroid%20and%20line%20width.%20The%20Doppler%20shift%20is%20defined%20to%20be%20zero%20at%20the%20limb%2C%20which%20yields%20a%20reference%20wavele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2023-12-05 at 2.46.39 PM.png","hash":"4e6d43f2917667a8ad1bf73041d345ed","mimeType":"image/png","caption":"Figure%202.%20Plots%20of%20intensity%20%28top%29%2C%20Doppler%20velocity%20%28middle%29%2C%20and%20non-thermal%20velocity%20%28bottom%29%20averaged%20over%20100%20equally-spaced%20bins%20in%20%CE%BC.%20Linear%20fits%20to%20the%20Doppler%20velocity%20and%20non-thermal%20velocity%20are%20overplotted%20in%20red%2C%20and%20the%20fit%20parameters%20are%20given%20in%20Table%201.%20The%20Pearson%20correlation%20coefficients%20%28PCC%29%2C%20R%2C%20are%20displayed%20on%20the%20middle%20and%20bottom%20panels.%20The%20blue%20points%20on%20the%20middle%20panel%20are%20from%20Peter%20%26amp%3B%20Judge%20%281999%29."},{"type":"text","text":"A%20similar%20procedure%20was%20applied%20to%20the%20coronal%20hole%20regions.%20Gaussian%20fits%20were%20performed%20to%20the%20Si%20IV%201402%20%26Aring%3B%20line%20in%20the%20coronal%20hole%2C%20and%20the%20parameters%20were%20then%20binned%20into%20uniformly-spaced%20%CE%BC%20bins.%0A%0AFigure%203%20shows%20the%20variations%20of%20intensity%2C%20Doppler%20velocity%20and%20non-thermal%20velocity%20as%20functions%20of%20%CE%BC.%20The%20Doppler%20velocity%20and%20non-thermal%20velocity%20are%20reasonably%20consistent%20with%20the%20quiet%20Sun%20results%2C%20and%20show%20linear%20variations%20with%20%CE%BC.%0A%0AThe%20Doppler%20velocity%20at%20disc%20centre%20is%204.8%20km%20s%3Csup%3E-1%3C%2Fsup%3E%20%28redshift%29.%20Peter%20%26amp%3B%20Judge%20%281999%29%20provided%20some%20measurements%20of%20Doppler%20velocities%20in%20coronal%20holes%2C%20but%20did%20not%20include%20Si%20IV.%20However%2C%20they%20had%20results%20for%20C%20IV%2C%20which%20is%20formed%20at%20a%20similar%20temperature%2C%20and%20these%20are%20plotted%20in%20blue%20on%20the%20middle%20panel.%20They%20found%20a%20small%20blueshift%20over%20a%20partial%20%CE%BC%20range%2C%20which%20is%20in%20disagreement%20with%20the%20present%20results.%0A%0AThe%20non-thermal%20velocity%20at%20the%20limb%20is%2024%20km%20s%3Csup%3E-1%3C%2Fsup%3E%2C%20consistent%20with%20the%20quiet%20Sun%20data.%20However%2C%20the%20disc%20centre%20value%20is%20larger%20at%2015%20km%20s%3Csup%3E-1%3C%2Fsup%3E.%20This%20suggests%20there%20may%20be%20enhanced%2C%20random%20longitudinal%20motions%20in%20the%20coronal%20hole%2C%20perhaps%20due%20to%20waves."},{"type":"image","file":"","url":"nuggetvideos/2023/12/02/pod_polito_vanessa_2023-12-02T00%3A55%3A35.896Z/Screenshot 2023-12-05 at 2.47.33 PM.png","hash":"5fab1f01b48ace138576d8476e29bb1a","mimeType":"image/png","caption":"Same%20as%20the%20previous%20Figure%20but%20for%20the%20coronal%20hole%20regions."}],"references":["This article: <a href=\"https://ui.adsabs.harvard.edu/abs/2023MNRAS.526..383K/abstract\">Kayshap, Pradeep & Young, Peter R., MNRAS, 526, 383</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1973A%26A....22..161B/abstract\">Boland B. C., Engstrom S. F. T., Jones B. B., Wilson R., 1973, A&A, 22, 161</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1976ApJ...205L.177D/abstract\">Doschek G. A., Feldman U., Bohlin J. D., 1976, ApJ, 205, L177</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1992str..book.....M/abstract\">Mariska J. T., 1992, The Solar Transition Region. Cambridge Univ. Press, Cambridge</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1999ApJ...522.1148P/abstract\">Peter H., Judge P. G., 1999, ApJ, 522, 1148</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022MNRAS.511.1383R/abstract\">Rao Y. K., Del Zanna G., Mason H. E., 2022, MNRAS, 511, 1383</a>","","","",""],"pubDate":"2023-12-13T01:32:03.106Z"},{"id":"pod_polito_vanessa_2023-10-23T09:21:32.106Z","submitter":"","author":"Graham S. Kerr [1,2], Adam F. Kowalski [3,4], Joel C. Allred [1], Adrian N. Daw [1] & Melissa R. Kane [3]","status":"published","creation-date":"2023-10-23T09:21:32.148Z","last-modified-date":"2023-11-14T21:26:21.01Z","credit":"[1] Heliophysics Science Division, NASA Goddard Space Flight Center [2] Department of Physics, Catholic University of America [3] Department of Astrophysical and Planetary Sciences, University of Colorado [4] National Solar Observatory","title":"An Optically Thin View of the Flaring Chromosphere: Nonthermal widths in a chromospheric condensation during an X-class solar flare","contentBlocks":[{"type":"text","text":"The%20bulk%20of%20solar%20flare%20energy%20is%20deposited%20in%20the%20chromosphere.%20Flare%20ribbons%20and%20footpoints%20in%20the%20chromosphere%20therefore%20offer%20great%20diagnostic%20potential%20of%20flare%20energy%20release%20and%20transport%20processes.%20High%20quality%20observations%20from%20the%20IRIS%20mission%20have%20transformed%20our%20view%20of%20the%20Sun%E2%80%99s%20atmospheric%20response%20to%20flares%20%28de%20Pontieu%20et%20al%202021%3B%20Kerr%202022%2C2023%29.%0A%0AReproducing%20certain%20aspects%20of%20the%20Mg%20II%20lines%20remain%20frustratingly%20out%20of%20reach%20in%20state-of-the-art%20flare%20models%2C%20which%20are%20unable%20to%20satisfactorily%20reproduce%20the%20very%20broad%20line%20profiles%20%28Rubio%20da%20Costa%20%26amp%3B%20Kleint%202017%3B%20Kerr%202023%29.%20A%20commonly%20proposed%20resolution%20to%20this%20is%20to%20assert%20that%20very%20large%20values%20of%20%E2%80%98microturbulence%E2%80%99%20is%20present.%20%0A%0AIn%20Kerr%20et%20al%20%282023%29%20we%20assessed%20the%20validity%20of%20that%20approach%20by%20analysing%20optically%20thin%20lines%20in%20the%20flare%20chromosphere%20from%20an%20X-class%20solar%20flare%2C%20using%20the%20derived%20value%20of%20nonthermal%20line%20widths%20%28upper%20limits%20on%20microturbulence%29%20as%20a%20constraint%20to%20our%20numerical%20models."},{"type":"image","file":"","url":"nuggetvideos/2023/10/23/pod_polito_vanessa_2023-10-23T09%3A21%3A32.106Z/IRISSJI_1330A_2014_Oct_25_0023.png","hash":"2238d130dbb9d1acffbbaab035fd508b","mimeType":"image/png","caption":"Figure%201%3A%20IRIS%201330%20SJI%20image%20of%20the%20X-class%202014%20October%2025%20solar%20flare.%20Our%20analysis%20focussed%20on%20spectra%20from%20the%20ribbon%20bounded%20by%20the%20blue%20box."},{"type":"text","text":"The%20X-class%20flare%20SOL2014-10-25T17%3A08%3A00%20was%20observed%20by%20IRIS%20in%20sit-and-stare%20mode%2C%20with%20full%20spectral%20readout%20providing%20high-cadence%20%285.36s%29%20observations%20of%20the%204%20lines%20of%20interest%2C%20not%20all%20of%20which%20are%20always%20so%20cleanly%20observed%20without%20the%20full%20readout%3A%20Mg%20II%2C%20O%20I%201355.598%26Aring%3B%2C%20Cl%20I%201351.6%26Aring%3B%2C%20and%20Fe%20II%202814.445%26Aring%3B.%20The%20latter%20three%20have%20been%20little%20studied%20in%20flares%2C%20and%20shared%20common%20characteristics%20during%20the%20flare%2C%20each%20increasing%20in%20intensity%20and%20exhibiting%20prominent%20red%20wing%20components%20that%20we%20attributed%20to%20a%20chromospheric%20condensation.%20Figure%201%20shows%20a%20context%20image%20from%20IRIS%E2%80%99%20slit-jaw%20imager%2C%20and%20Figure%202%20shows%20the%20flare%20spectra."},{"type":"image","file":"","url":"nuggetvideos/2023/10/23/pod_polito_vanessa_2023-10-23T09%3A21%3A32.106Z/combined_wavetime.png","hash":"5731e90886d271acc40357cb00ed4be3","mimeType":"image/png","caption":"Figure%202%3A%20The%20temporal%20evolution%20of%20emission%20from%20the%20source%20of%20interest%2C%20with%20cut-outs%20showing%20individual%20spectral%20in%20more%20detail.%20Shown%20are%20the%20Cl%20I%201351.657%20%26Aring%3B%20%28top%20left%29%2C%20O%20I%201355.598%26Aring%3B%20%28top%20right%3B%20window%20also%20contains%20the%20C%20I%201355.8%26Aring%3B%20line%29%2C%20Mg%20II%20k%20%28bottom%20left%29%20and%20Fe%20II%202814.445%20%26Aring%3B%20%28bottom%20right%3B%20window%20also%20contains%20an%20Fe%20I%20line%29.%20In%20each%20wavelength-time%20diagram%20the%20horizontal%20lines%20indicate%20the%20times%20of%20the%20cut-outs%2C%20and%20the%20times%20are%20shown%20as%20seconds%20from%20t0.%20A%20weak%20red-wing%20component%20is%20present%20in%20each%20spectra%2C%20e.g.%20around%20t%20%3D%20284%20s%2C%20which%20shows%20up%20more%20clearly%20in%20the%20narrower%20lines."},{"type":"text","text":"Quiet%20sun%20modelling%20of%20O%20I%201355.598%26Aring%3B%20%28Lin%20%26amp%3B%20Carlsson%202015%29%20suggests%20an%20optically%20thin%20formation%20%28albeit%20requiring%20radiation%20transfer%20modelling%20due%20to%20the%20importance%20of%20charge%20exchange%20in%20the%20O%20I%20ionisation%20fraction%29%2C%20so%20given%20their%20similarity%20to%20flaring%20O%20I%20behaviour%20we%20worked%20under%20the%20assumption%20that%20at%20least%20the%20shifted%20components%20of%20the%20Fe%20II%20and%20Cl%20I%20lines%20could%20also%20be%20optically%20thin.%20Our%20subsequent%20modelling%20efforts%20confirmed%20this%20assumption%3A%20O%20I%201355.598%26Aring%3B%20remained%20optically%20thin%20throughout%20the%20flare%2C%20and%20though%20the%20line%20core%20occasionally%20suffered%20from%20optical%20depth%20effects%2C%20the%20shifted%20red%20wing%20component%20of%20Fe%20II%202814.445%26Aring%3B%20was%20optically%20thin.%20For%20three%20pixels%20in%20the%20flare%20ribbon%20of%20interest%20we%20fit%20two%20Gaussian%20components%20to%20the%20O%20I%2C%20Cl%20I%20and%20Fe%20II%20lines%2C%20finding%20that%20the%20redshifted%20components%20became%20briefly%20broadened%20during%20the%20flare%2C%20Values%20of%20nonthermal%201%2Fe%20half-widths%20were%20in%20the%20range%205-12%20km%20s%3Csup%3E%E2%88%921%3C%2Fsup%3E%2C%20with%20a%20characteristic%20value%20of%2010%20km%20s%3Csup%3E%E2%88%921%3C%2Fsup%3E.%20Figure%203%20shows%20the%20nonthermal%20widths%20and%20Doppler%20shifts%20of%20each%20line%2C%20where%20the%20error%20bars%20are%20from%20a%20Monte-Carlo%20analysis."},{"type":"image","file":"","url":"nuggetvideos/2023/10/23/pod_polito_vanessa_2023-10-23T09%3A21%3A32.106Z/IRISSG_OI_2014_Oct_25_MetricsDG_AllLines_R1_wErrorsMCpost_ForPaper.png","hash":"51a420b696df5778a3ab06169791e98b","mimeType":"image/png","caption":"Figure%203%3A%20Comparing%20the%20Doppler%20shift%20%28firstcolumn%29%20and%20nonthermal%20line%20width%20%28second%20column%29%20of%20the%20shifted%20component%20%28the%20condensation%29%20obtained%20for%20the%20O%20I%201355.598%20%26Aring%3B%20%28green%20%E2%9E%95%20symbols%29%2C%20Cl%20I%201351.657%20%26Aring%3B%20%28orange%20%E2%97%8F%20symbols%29%2C%20and%20Fe%20II%202814.445%20%26Aring%3B%20%28grey%20%E2%96%A0%20symbols%29.%20Each%20row%20shows%20the%20metrics%20for%20a%20different%20slit%20position.%20Error%20bars%20are%20from%20a%20Monte%20Carlo%20analysis%20of%20each%20profile."},{"type":"text","text":"Using%20nonthermal%20electron%20distribution%20parameters%20derived%20from%20%3Cem%3EFermi%3C%2Fem%3E%2FGBM%20data%20by%20Kowalski%20et%20al%20%282019%29%2C%20we%20produced%20radiation%20hydrodynamic%20flare%20simulations%20using%20the%20RADYN%20code%20%28Allred%20et%20al%202015%29.%20Those%20flare%20atmospheres%20were%20used%20as%20input%20to%20the%20RH15D%20radiation%20transfer%20code%20to%20synthesise%20Mg%20II%20and%20O%20I.%20Fe%20II%20was%20synthesised%20following%20the%20approach%20of%20Kowalski%20et%20al%20%282017%29.%20Within%20the%20chromospheric%20condensations%20%28dense%20downflowing%20regions%29%20we%20included%20a%20nonthermal%20broadening%20value%20of%2010%20km%20s%3Csup%3E%E2%88%921%3C%2Fsup%3E%20to%20mimic%20the%20observations.%20The%20assumption%20here%2C%20of%20course%2C%20is%20that%20Mg%20II%20would%20experience%20the%20same%20magnitude%20of%20microturbulence%20as%20O%20I%2C%20Fe%20II%20and%20Cl%20I.%20That%20is%2C%20that%20they%20form%20relatively%20close%20to%20each%20other%20in%20the%20flare%20atmosphere.%20Our%20modelling%20confirmed%20this%20assumption%20was%20valid.%20The%20flare%20chromosphere%20became%20sufficiently%20compressed%20such%20that%20the%20shifted%20components%20of%20the%20three%20narrow%20lines%20formed%20within%20a%20few%2010s%20of%20km%20of%20Mg%20II.%20We%20also%20assumed%20that%20there%20is%20not%20significant%20microturbulence%20at%20depths%20below%20the%20condensation%2C%20since%20the%20lines%E2%80%99%20stationary%20components%20are%20relatively%20narrow.%20%0A%0AFigure%204%20shows%20the%20model-data%20comparison.%20Our%20synthetic%20O%20I%20spectra%20were%20remarkably%20consistent%20with%20the%20observations%2C%20showing%20comparable%20intensities%20when%20degraded%20to%20IRIS%20count%20rates%20and%20resolution%2C%20as%20well%20as%20similar%20red%20wing%20asymmetries%20and%20line%20widths.%20The%20Fe%20II%20line%20was%20too%20intense%20but%20we%20discuss%20in%20Kerr%20et%20al%20%282023%29%20why%20we%20think%20this%20is%20the%20case.%20Although%20the%20general%20properties%20of%20the%20Mg%20II%20lines%20were%20well%20captured%20%28red%20shifts%2C%20relative%20line-to-continuum%20intensity%2C%20subordinate%20line%20ratios%20etc.%2C%29%20the%20synthetic%20line%20widths%20%3Cem%3Ewere%20still%20too%20narrow%20compared%20to%20the%20observations%3C%2Fem%3E."},{"type":"image","file":"","url":"nuggetvideos/2023/10/23/pod_polito_vanessa_2023-10-23T09%3A21%3A32.106Z/combined_modeldata.png","hash":"912277ed597c0aa262018f9054da0f51","mimeType":"image/png","caption":"Figure%204%3A%20Model-data%20comparisons%20of%20IRIS%20spectral%20lines.%20In%20each%20panel%20black%20lines%20are%20IRIS%20observations%2C%20orange%20lines%20are%20from%20the%20a%20%27weaker%27%20%285F10%29%20flare%20simulation%2C%20and%20green%20lines%20are%20a%20%27stronger%27%20%282F11%29%20simulation%2C%20both%20degraded%20using%20the%20IRIS%20response%2C%20exposure%20times%20and%20pixel%20summing.%20Additionally%2C%20yellow%20lines%20show%20the%20NUV%20spectra%20%28Mg%20II%20and%20Fe%20II%29%20from%20the%202F11%20simulation%20scaled%20down%20by%20a%20factor%20of%206.%20The%20top%20row%20shows%20the%20O%20I%2C%20and%20Fe%20II%20lines%2C%20where%20the%20pre-flare%20intensity%20and%20continuum%20have%20been%20subtracted.%20The%20bottom%20row%20shows%20the%20Mg%20II%20NUV%20spectra.%20The%20main%20takeaway%20points%20here%20are%20that%20O%20I%20has%20a%20rather%20good%20model-data%20comparison.%20Fe%20II%20line%20shapes%20are%20OK%2C%20but%20the%20lines%20themselves%20are%20far%20too%20intense.%20Regarding%20Mg%20II%2C%20although%20the%202F11%20simulation%20is%20%7E6%20X%20too%20intense%2C%20the%20Mg%20II%20subordinate%20lines%20and%20local%20continuum%20are%20otherwise%20reasonably%20well%20captured.%20The%20Mg%20II%20resonance%20lines%20are%2C%20however%2C%20still%20not%20broad%20enough%20on%20either%20side%20of%20the%20line%20core%2C%20and%20the%20broadening%20in%20the%20line%20core%20is%20somewhat%20too%20large."},{"type":"text","text":"Our%20study%20demonstrates%20that%20careful%20data-guided%20simulations%20of%20the%20chromospheric%20response%20to%20a%20solar%20flares%20revealed%20that%20our%20models%20are%20still%20missing%20important%20ingredients%20since%20they%20are%20as-yet%20unable%20to%20reproduce%20the%20observed%20Mg%20II%20line%20widths.%20We%20speculate%20that%20a%20promising%20candidate%20is%20heating%20to%20greater%20depth%20than%20electron-beam%20driven%20flare%20simulations%20can%20seemingly%20achieve.%0A%0ARecent%20efforts%20%28Sainz%20Dalda%20%26amp%3B%20De%20Pontieu%202022%29%20used%20spectral%20inversions%20to%20explore%20broad%20Mg%20II%20lines%2C%20producing%20model%20atmospheres%20that%20had%20mictroturbulent%20broadening%20%E2%88%BC%205%20%E2%88%92%2015%20km%20s%3Csup%3E%E2%88%921%3C%2Fsup%3E%20in%20the%20chromosphere.%20Whilst%20these%20values%20are%20consistent%20with%20our%20findings%2C%20the%20atmospheres%20on%20first%20glance%20appear%20quite%20different%20that%20those%20produced%20by%20electron%20beam%20driven%20radiation%20hydrodynamic%20simulations.%20Sainz%20Dalda%20%26amp%3B%20De%20Pontieu%20%282022%29%20also%20state%20that%20it%20is%20the%20presence%20of%20a%20strong%2C%20divergent%20velocity%20field%20in%20the%20upper%20chromosphere%20of%20their%20inverted%20atmospheres%20that%20produces%20the%20%E2%80%98pointy%E2%80%99%2C%20very%20broad%20Mg%20II%20profiles%20%28though%20not%20as%20extreme%20as%20that%20required%20by%20Rubio%20da%20Costa%20%26amp%3B%20Kleint%202017%29.%20However%2C%20it%20is%20not%20clear%20then%20why%20radiation%20hydrodynamics%20models%20that%20calculate%20velocity%20gradients%20and%20mass%20advection%20self-consistently%2C%20and%20which%20often%20contain%20strong%20upflow%20and%20downflow%20gradients%2C%20do%20not%20similarly%20reproduce%20these%20profiles.%20We%20look%20forward%20to%20the%20opportunity%20to%20comprehensively%20compare%20our%20RADYN%20model%20atmospheres%20with%20the%20results%20of%20spectral%20inversions."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...809..104A/abstract\">Allred, J.C. et al., The Astrophysical Journal, Volume 809, Issue 1 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021SoPh..296...84D/abstract\">de Pontieu, B. et al., Solar Physics, Volume 296, Issue 5 (2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022FrASS...960856K/abstract\">Kerr, G.S., Frontiers in Astronomy and Space Sciences, Vol. 9, article id. 1060856 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023FrASS...960862K/abstract\">Kerr, G.S., Frontiers in Astronomy and Space Sciences, Vol. 9, article id. 1060862 (2023)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023MNRAS.tmp.3017K/abstract\">Kerr, G.S., et al., Monthly Notices of the Royal Astronomical Society, Advance Access (2023)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...878..135K/abstract\">Kowalski, A.F. et al., The Astrophysical Journal, Volume 878, Issue 2 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...836...12K/abstract\">Kowalski, A.F. et al., The Astrophysical Journal, Volume 836, Issue 1 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...813...34L/abstract\">Lin, H.H. and Carlsson, M., The Astrophysical Journal, Volume 813, Issue 1 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...842...82R/abstract\">Rubio da Costa, F. and Kleint, L., The Astrophysical Journal, Volume 842, Issue 2 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023FrASS..1033429S/abstract\">Sainz Dalda, A. and de Pontieu, B., Frontiers in Astronomy and Space Sciences, vol. 10, id. 1133429 (2023)</a>"],"pubDate":"2023-11-14T21:04:29.287Z"},{"id":"pod_polito_vanessa_2023-09-20T17:00:28.068Z","submitter":"Helle Bakke","author":"Helle Bakke[1, 2], Lars Frogner[1, 2], Luc Rouppe van der Voort[1, 2], Boris V. Gudiksen[1, 2], Mats Carlsson[1, 2]","status":"published","creation-date":"2023-09-20T17:00:28.101Z","last-modified-date":"2023-09-29T07:38:32.576Z","credit":"[1] Institute of Theoretical Astrophysics, University of Oslo, P.O.Box 1029 Blindern, N-0315 Oslo, Norway, [2] Rosseland Centre for Solar physics, University of Oslo, P.O.Box 1029 Blindern, N-0315 Oslo, Norway","title":"Accelerated particle beams in a 3D simulation of the quiet Sun. Lower atmospheric spectral diagnostics","contentBlocks":[{"type":"text","text":"Nanoflares%20are%20small-scale%20heating%20events%20associated%20with%20magnetic%20reconnection%20in%20the%20solar%20atmosphere.%20With%20their%20relatively%20low%20energy%20releases%2C%20they%20are%20believed%20to%20occur%20frequently%20throughout%20the%20atmosphere%20and%20consistently%20heat%20the%20corona%2C%20forming%20the%20basis%20of%20the%20nanoflare%20theory%3B%20a%20heating%20mechanism%20that%20can%20potentially%20explain%20the%20extreme%20temperature%20increase%20from%20a%20few%20thousand%20Kelvin%20in%20the%20photosphere%20to%20millions%20of%20degrees%20in%20the%20corona%20%28Parker%201988%29.%20Unfortunately%2C%20this%20theory%20has%20been%20difficult%20to%20prove%20as%20the%20energy%20released%20from%20nanoflares%20are%20below%20the%20detection%20threshold%20of%20current%20instrumentation%2C%20leaving%20the%20presence%20and%20properties%20of%20nanoflares%20in%20the%20solar%20atmosphere%20poorly%20known.%20%0A%0ASo%20how%20can%20we%20determine%20the%20role%20of%20nanoflares%20in%20the%20solar%20atmosphere%20without%20observational%20proof%3F%20In%20this%20work%2C%20we%20investigated%20potential%20signatures%20of%20nanoflares%20in%20a%203D%20Bifrost%20simulation%20%28Gudiksen%20et%20al.%202011%29%20that%20includes%20accelerated%20electrons%20%28Bakke%20et%20al.%202018%3B%20Frogner%20et%20al.%202020%3B%20Frogner%20%26amp%3B%20Gudiksen%202022%29.%20It%20is%20generally%20accepted%20that%20during%20magnetic%20reconnection%2C%20energy%20released%20from%20flares%20is%20transported%20by%20electrons%20accelerated%20to%20non-thermal%20energies.%20The%20electrons%20lose%20energy%20through%20collisions%20with%20the%20ambient%20plasma%20as%20they%20travel%20along%20the%20magnetic%20field%2C%20giving%20rise%20to%20signatures%20in%20the%20spectral%20lines%20forming%20at%20the%20sites%20where%20the%20energy%20is%20deposited.%20We%20used%20this%20knowledge%20to%20explore%20the%20impact%20of%20non-thermal%20electrons%20in%20Bifrost%20by%20analysing%20synthetic%20spectral%20lines%2C%20namely%20the%20chromospheric%20Ca%20II%20854.2%20nm%2C%20Ca%20II%20H%26amp%3BK%2C%20and%20Mg%20II%20h%26amp%3Bk%20lines%20as%20well%20as%20the%20transition%20region%20%28TR%29%20Si%20IV%20resonance%20lines.%20The%20selected%20spectra%20were%20chosen%20based%20on%20the%20capabilities%20of%20current%20instrumentation%2C%20i.e.%20IRIS%20%28De%20Pontieu%20et%20al.%202014%29%20which%20can%20observe%20the%20Si%20and%20Mg%20lines%2C%20in%20order%20to%20give%20further%20guidance%20to%20future%20observations."},{"type":"image","file":"","url":"nuggetvideos/2023/09/20/pod_polito_vanessa_2023-09-20T17%3A00%3A28.068Z/figure_1.png","hash":"cf08fa27023c966ab06cbf3b368b2fa1","mimeType":"image/png","caption":"Figure%201.%20Integrated%20average%20beam%20heating%20power%20along%20the%20z-axis%20%28upper%20panel%29%20and%20y-axis%20%28lower%20panel%29%20of%20the%20Bifrost%20simulation%2028%20s%20after%20the%20electrons%20have%20been%20injected.%20Blue%20regions%20represent%20electron%20acceleration%20sites%2C%20and%20orange%20regions%20represent%20plasma%20heating%20from%20the%20energy%20deposited%20by%20the%20electrons.%20The%20coloured%20circles%20in%20the%20upper%20panel%20are%20areas%20of%20interest%2C%20while%20crosses%20%28upper%20panel%29%20and%20dashed%20lines%20%28lower%20panel%29%20are%20the%20specific%20locations%20analysed%20in%20detail%20%28L1%2C%20L2%2C%20L3%2C%20and%20L4%29."},{"type":"text","text":"We%20chose%20four%20different%20regions%20of%20the%20simulation%20that%20are%20both%20subject%20and%20not%20subject%20to%20electron%20beams.%20These%20regions%20can%20be%20seen%20in%20Figure%201%2C%20where%20L1%20is%20located%20in%20a%20region%20without%20electron%20beams%20and%20L2%2C%20L3%2C%20and%20L4%20are%20located%20at%20different%20magnetic%20field%20footpoints%20and%20are%20subject%20to%20beam%20heating.%20In%20order%20to%20get%20an%20idea%20of%20the%20atmospheric%20response%20to%20the%20electron%20beams%2C%20we%20investigated%20the%20evolution%20of%20temperature%2C%20vertical%20velocity%2C%20electron%20number%20density%2C%20and%20beam%20heating%20rate%20at%20the%20four%20locations.%20The%20temporal%20evolution%20of%20the%20parameters%20can%20be%20seen%20in%20Figure%202%2C%20where%20we%20note%20that%20the%20evolution%20is%20taken%20along%20the%20z-axis%20as%20seen%20from%20directly%20above%2C%20and%20not%20along%20the%20magnetic%20field%20lines.%20That%20means%20that%20the%20increase%20in%20beam%20heating%20rate%20as%20seen%20in%20panels%20%28n%29-%28p%29%20do%20not%20necessarily%20originate%20from%20vertical%20field%20lines%20aligned%20with%20z%2C%20but%20instead%20from%20reconnection%20events%20along%20the%20magnetic%20field%20connected%20to%20the%20footpoints.%20Even%20though%20we%20cannot%20make%20a%20conclusion%20about%20the%20reconnection%20sites%2C%20Figure%202%20provides%20aid%20in%20terms%20of%20the%20atmospheric%20response%20to%20the%20localised%20heating%20at%20TR%20and%20chromospheric%20heights."},{"type":"image","file":"","url":"nuggetvideos/2023/09/20/pod_polito_vanessa_2023-09-20T17%3A00%3A28.068Z/figure_2.png","hash":"ecfbf64fa01aae805bed383a7e5aee68","mimeType":"image/png","caption":"Figure%202.%20Evolution%20of%20temperature%2C%20vertical%20velocity%2C%20electron%20number%20density%2C%20and%20beam%20heating%20rate%20in%20the%20Bifrost%20simulation.%20The%20quantities%20are%20plotted%20along%20z%20with%201%20s%20intervals%20for%20the%20duration%20of%20the%20simulation%20%28see%20colorbar%29%2C%20and%20each%20column%20represents%20the%20specific%20locations%20of%20interest.%20Negative%20%28positive%29%20velocities%20correspond%20to%20upflows%20%28downflows%29."},{"type":"text","text":"Further%2C%20we%20investigated%20the%20temporal%20evolution%20of%20the%20spectral%20lines%20as%20seen%20in%20Figure%203.%20The%20figure%20shows%20the%20evolution%20of%20Ca%20II%20854.2%20nm%2C%20Ca%20II%20H%2C%20Mg%20II%20k%2C%20and%20Si%20IV%20140.3%20nm%20at%20the%20four%20selected%20locations.%20The%20strongest%20emission%20of%20the%20spectra%20is%20found%20at%20L2%2C%20which%20is%20located%20at%20the%20magnetic%20field%20footpoint%20that%20is%20connected%20to%20the%20longest%20coronal%20loops%20where%20a%20large%20number%20of%20electron%20acceleration%20sites%20are%20present%20%28see%20the%20upper%20panel%20of%20Figure%201%29.%20The%20emission%20of%20the%20spectra%20at%20L3%20is%20weaker%20in%20comparison%20to%20both%20L2%20and%20L4%2C%20but%20the%20spectral%20lines%20are%20subject%20to%20shock%20waves%20passing%20through%20the%20atmosphere%20causing%20the%20oscillating%20patterns.%20Oscillations%20can%20also%20be%20seen%20in%20the%20Si%20IV%20line%20at%20the%20L4%20location%20up%20until%20around%2026%20s%2C%20after%20which%20the%20temperature%20at%20its%20formation%20height%20stabilises%20and%20the%20profile%20becomes%20similar%20to%20the%20initial%20profile."},{"type":"image","file":"","url":"nuggetvideos/2023/09/20/pod_polito_vanessa_2023-09-20T17%3A00%3A28.068Z/figure_3.png","hash":"59b1b151cf5f44111ab84937a1b6db5d","mimeType":"image/png","caption":"Figure%203.%20Temporal%20evolution%20of%20the%20Ca%20II%20854.2%20nm%2C%20Ca%20II%20H%2C%20Mg%20II%20k%2C%20and%20Si%20IV%20140.3%20nm%20spectral%20lines%20at%20the%20locations%20of%20interest.%20The%20orange%20profiles%20are%20taken%20at%20the%20first%20timestep%20after%20the%20electrons%20are%20injected%2C%20where%20the%20highest%20%28lowest%29%20intensity%20of%20the%20profiles%20in%20each%20row%20corresponds%20to%20the%20maximum%20%28minimum%29%20intensity%20of%20the%20respective%20colorbars.%20The%20x-axes%20are%20in%20units%20of%20Doppler%20offset%2C%20where%20negative%20%28positive%29%20velocities%20indicate%20blueshifts%20%28redshifts%29."},{"type":"text","text":"Apart%20from%20the%20oscillations%2C%20the%20temporal%20changes%20are%20relatively%20small%20and%20it%20is%20difficult%20to%20determine%20if%20the%20changes%20we%20see%20are%20caused%20by%20non-thermal%20electrons.%20However%2C%20we%20do%20see%20a%20clear%20difference%20between%20the%20spectra%20forming%20in%20regions%20subject%20to%20beams%20and%20not.%20Following%20the%20calculation%20of%20the%20contribution%20function%20to%20the%20line%20intensity%20in%20Carlsson%20%26amp%3B%20Stein%20%281997%29%2C%20we%20investigated%20the%20formation%20of%20the%20spectra%20in%20order%20to%20determine%20to%20what%20extent%20the%20lines%20are%20affected%20by%20changes%20in%20the%20atmosphere.%20We%20found%20that%20the%20spectral%20lines%20are%20highly%20affected%20by%20variations%20in%20temperature%20and%20vertical%20velocity.%20However%2C%20due%20to%20the%20complexity%20of%20the%20atmospheric%20response%20in%20Bifrost%20it%20is%20difficult%20to%20determine%20if%20specific%20signatures%20in%20the%20spectral%20lines%20arise%20uniquely%20from%20non-thermal%20electrons.%20Even%20though%20we%20cannot%20make%20a%20firm%20conclusion%20about%20the%20role%20of%20non-thermal%20electrons%20in%20the%20simulation%2C%20our%20spectral%20analysis%20can%20still%20contribute%20to%20the%20understanding%20of%20small-scale%20events%20in%20the%20solar%20atmosphere."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1988ApJ...330..474P/abstract\"> Parker, E. N., ApJ 330, 474 (1988)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2011A%26A...531A.154G/abstract\"> Gudiksen, B. V., Carlsson, M., Hansteen, V. H., et al., A&A 531, 154 (2011)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018A%26A...620L...5B/abstract\"> Bakke, H., Frogner, L., Gudiksen, B. V., A&A 620, 5 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...643A..27F/abstract\"> Frogner, L., Gudiksen, B. V., Bakke, H., A&A 643, 27 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022arXiv221001609F/abstract\"> Frogner, L. & Gudiksen, B. V., arXiv (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\"> De Pontieu, B., Title, A. M., Lemen, J. R., et al., SoPh 289, 2733 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1997ApJ...481..500C/abstract\"> Carlsson, M. & Stein, R. F., ApJ 481, 500 (1997)</a>","","",""],"pubDate":"2023-10-09T12:44:30.973Z"},{"id":"pod_polito_vanessa_2023-08-25T21:28:28.536Z","submitter":"Yan Xu","author":"Yan Xu [1,2], Graham S. Kerr [3,4], Vanessa Polito [5,6], Nengyi Huang [1,2], Ju Jing [1,2] and Haimin Wang [1,2]","status":"published","creation-date":"2023-08-25T21:28:28.539Z","last-modified-date":"2023-09-13T01:04:43.507Z","credit":"1. Institute for Space Weather Sciences, New Jersey Institute of Technology 2. Big Bear Solar Observatory, New Jersey Institute of Technology 3. NASA Goddard Space Flight Center, Heliophysics Science Division 4. Department of Physics, Catholic University of America 5. Bay Area Environmental Research Institute 6. Lockheed Martin Solar and Astrophysics Laboratory","title":"Extreme Red-wing Enhancements of UV Lines During the 2022 March 30 X1.3 Solar Flare","contentBlocks":[{"type":"text","text":"Flare%20heating%20in%20the%20lower%20solar%20atmosphere%20leads%20to%20strong%20temperature%20gradients.%20%20The%20pressure%20imbalance%20following%20rapid%20heating%20drives%20fast%20flows%20of%20mass%20both%20upwards%20and%20downwards%2C%20known%20as%20chromospheric%20evaporations%20and%20condensations%2C%20respectively.%20Usually%20the%20upward%20velocity%20is%20faster%20than%20100%20km%2Fs%20and%20can%20reach%20to%20350%20km%2Fs%20in%20Fe%20XXI%201354.1%20%26Aring%3B%20line%20%28Tian%20%26amp%3B%20Chen%202018%3B%20and%20Polito%20et%20al.%202015%29%2C%20and%20500%20km%2Fs%20in%20X-ray%20%28Ning%20et%20al.%202009%2C%20%20Zhang%20%26amp%3B%20Ji%202013%29.%20In%20contrast%2C%20chromospheric%20condensations%20%28that%20propagate%20into%20denser%20plasma%29%20are%20usually%20slower%2C%20about%2010%20to%20100%20km%2Fs%28Ichimoto%20%26amp%3B%20Kurokawa%201984%3B%20Fisher%20et%20al.%201985%29.%20High%20spatial%2C%20spectral%2C%20and%20temporal%20Observations%20by%20IRIS%20found%20a%20similar%20speed%20range%20in%20Si%20IV%20and%20Mg%20II%20lines%20%28Kerr%20et%20al.%202015%3B%20Wang%20et%20al.%202023%29.%20%0A%0AIn%20this%20study%2C%20we%20present%20IRIS%20observations%20of%20a%20localized%20source%20during%20the%20X1.3%20flare%20on%202022%20March%2030.%20Spectral%20lines%20originating%20from%20this%20source%20exhibit%20extremely%20large%20red%20wings%2C%20from%20which%20we%20infer%20strong%20red-shifts%20in%20the%20transition%20region%20and%20upper%20chromosphere%20at%20speeds%20exceeding%20100%20km%2Fs.%20Figure%201%20shows%20the%20IRIS%20SJI%202796%20%26Aring%3B%20image%20alongside%20the%20light%20curves%20of%20our%20source%20of%20interest%20%28SOI%29.%20The%20SOI%20brightens%20twice%2C%20where%20the%20first%20peak%20is%20in%20response%20to%20the%20passing%20of%20the%20major%20flare%20ribbon.%20The%20second%20peak%2C%20very%20transient%2C%20is%20caused%20by%20a%20%20second%20heating%20event%2C%20that%20is%20seemingly%20associated%20with%20significantly%20faster%20downflows."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/nugget1.png","hash":"f6e0865824611aeabb042274588275a7","mimeType":"image/png","caption":"Fig.%201%20Left%20panel%3A%20IRIS%20SJI%202796%20%26Aring%3B%20at%2017%3A35%3A12%20UT.%20The%20red%20box%20indicates%20the%20source%20of%20interest%20%28SOI%29.%20Right%20panel%3A%20Light%20curves%20of%20GOES%20soft%20X-ray%20%28SXR%2C%20in%20black%29%2C%20derivative%20of%20SXR%20%28red%29%2C%20UV-2796%20in%20SOI%20%28green%29."},{"type":"text","text":"We%20used%20two%20methods%20to%20infer%20the%20magnitude%20of%20the%20chromospheric%20downflows%3A%20spectral%20moments%20and%20multiple-component%20Gaussian%20fits.%20Figure%202%20shows%20examples%20using%20multiple-component%20Gaussian%20fits%20of%20Mg%20II%2C%20C%20II%20and%20Si%20IV%20lines%20at%2017%3A35%3A19%20UT%20%28from%20when%20the%20red-wing%20asymmetry%20was%20largest%29.%20Those%20results%20suggest%20a%20large-scale%20motion%20with%20a%20speed%20up%20to%20%20160%20km%2Fs%20in%20the%20upper%20chromosphere%20and%20transition%20region.%20During%20the%20peak%20time%20%2817%3A35%3A19%20to%2017%3A35%3A29%20UT%29%2C%20the%20Mg%20II%20subordinate%20triplet%20also%20exhibit%20red-wing%20components%2C%20that%20start%20as%20separate%20components%20which%20merge%20with%20the%20stationary%20component%20%28similar%20to%20the%20chromospheric%20condensations%20studied%20by%20Graham%20et%20al%202020%2C%20though%20with%20much%20a%20larger%20Doppler%20speed%29%20.%20Their%20Doppler%20shift%20at%2017%3A35%3A19%20UT%20was%20measured%20to%20be%20130%20km%2Fs."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/nugget2.png","hash":"1f1d76799308ae54f582759f2f0c9834","mimeType":"image/png","caption":"Fig.%202%20Multi-Gaussian%20fit%20of%20UV%20spectra%20at%2017%3A35%3A19%20UT%20on%20SOI%20%28Y%20%3D%2051%20pixel%29.%20Three%20Gaussian%20components%20are%20involved%20and%20the%20combinations%20of%20all%20components%20are%20modeled%20results%20in%20red%20solid%20curves.%20The%20dotted-dash%20line%20in%20yellow%20is%20the%20red-most%20Gaussian%20fit%2C%20representing%20the%20downward%20Doppler%20velocities.%20The%20vertical%20lines%20show%20the%20rest%20line%20center%20positions%20of%20C%20II%2C%20Si%20IV%20and%20Mg%20II."},{"type":"text","text":"The%20moments%20analysis%20provides%20an%20averaged%20Doppler%20speed%20over%20the%20full%20line%20so%20yields%20smaller%20Doppler%20shifts%20for%20each%20line%20than%20the%20results%20obtained%20by%20multiple-component%20Gaussian%20fitting.%20Still%2C%20those%20moments-derived%20Doppler%20speeds%20are%20larger%20than%20typically%20observed%20flare%20sources.%20A%20histogram%20of%20Mg%20II%20Doppler%20shifts%20derived%20from%20the%20moments%20analysis%20including%20pixels%20in%20both%20SOI%20%28blue%29%20and%20the%20main%20flare%20ribbon%20%28orange%29%20is%20shown%20in%20Figure%203.%20On%20the%20flare%20ribbon%20%28pixels%2027%20to%2048%29%2C%20the%20peak%20shift%20is%20around%2030%20km%2Fs.%20Most%20of%20the%20redshifts%20of%20SOI%20pixels%20range%20from%2050%20to%20nearly%2090%20km%2Fs%20.%20For%20those%20pixels%20in%20the%20SOI%20with%20large%20moments-derived%20Doppler%20shifts%20our%20Gaussian%20fitting%20analysis%20yields%20Doppler%20motions%20far%20into%20the%20wings%2C%20up%20to%20160%20km%2Fs.%20The%20temporal%20variation%20of%20the%20Doppler%20shifts%20are%20shown%20in%20Figure%204."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/f09.png","hash":"f687c5749bca99e26f8db2b822df6c46","mimeType":"image/png","caption":"Fig.%203%20Histogram%20of%20Mg%20II%20red-shifts%20of%20pixels%20on%20flare%20ribbon%20%28orange%29%20and%20SOI%20region%20%28blue%29."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/fig_temporal.png","hash":"c717d5130a7000e205d69416d9d51d94","mimeType":"image/png","caption":"Fig.%204%20Evolution%20of%20derived%20red-shift%20velocities%2C%20using%20multi-Gaussian%20fit%20in%20panels%20%28a%29%20-%20%28d%29%20and%20spectral%20moment%20method%20in%20panel%20%28e%29%20-%20%28h%29%2C%20on%20SOI%20%28Y%20%3D%2051%20pixel%29."},{"type":"text","text":"In%20addition%20to%20the%20Mg%20II%2C%20C%20II%20and%20Si%20IV%20lines%2C%20nearby%20weaker%20lines%20are%20studied.%20The%20O%20I%20line%20at%201355.598%20%26Aring%3B%20exhibits%20no%20extraordinary%20red%20wing%20asymmetries%2C%20and%20remains%20relatively%20weak.%20As%20this%20line%20forms%20deeper%20than%20Mg%20II%20lines%2C%20the%20absence%20of%20red%20shift%20strongly%20implies%20that%20the%20unusually%20strong%20Doppler%20shift%20discussed%20above%20is%20confined%20to%20the%20transition%20region%20and%20upper%20chromosphere.%20Furthermore%2C%20the%20Mg%20II%20subordinate%20lines%20are%20strongly%20in%20emission%20and%20also%20exhibit%20asymmetries.%20This%20result%20suggests%20a%20similar%20scenario%20of%20chromospheric%20condensation%20described%20in%20Graham%20et%20al.%2C%20%282020%29.%20We%20speculate%20that%20this%20observation%20is%20an%20extreme%20example%20of%20a%20dense%20chromospheric%20condensation.%20%20%20This%20condensation%20subsequently%20propagates%20through%20the%20transition%20region%20and%20chromosphere%20but%20is%20damped%20in%20the%20mid-upper%20chromosphere.%20Its%20maximum%20speed%20is%20at%20odds%20with%20both%20typical%20observations%20and%20also%20typical%20modeling%20of%20chromospheric%20condensations.%20Though%20flare%20radiation%20hydrodynamic%20models%20do%20suggest%20such%20large%20downflowing%20velocities%20can%20be%20produced%2C%20they%20are%20thus%20far%20too%20transient%20and%20subside%20to%20a%20few%2010s%20km%2Fs%20upon%20accruing%20mass%20in%20the%20upper%20chromosphere%20%28c.f.%20the%20flare%20loop%20modeling%20review%20by%20Kerr%202022%29.%20Modeling%20of%20%20the%20flaring%20chromosphere%20should%20endeavor%20to%20explore%20the%20conditions%20%28e.g.%20an%20unusually%20low%20density%29%20that%20lead%20to%20these%20supersonic%20downflows%2C%20with%20the%20fact%20that%20this%20source%20occurred%20in%20a%20previously%20heated%20atmosphere%20is%20perhaps%20important.%20For%20more%20information%20about%20this%20work%2C%20see%20Xu%20et%20al.%202023."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1985ApJ...289..414F/abstract\">Fisher, G. H., Canfield, R. C., & McClymont, A. N. 1985, 710 ApJ, 289, 414</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...895....6G/abstract\">Graham, D. R., Cauzzi, G., Zangrilli, L., et al. 2020, ApJ, 895, 6</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1984SoPh...93..105I/abstract\">Ichimoto, K., & Kurokawa, H. 1984, SoPh, 93, 105</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015A%26A...582A..50K/abstract\">Kerr, G. S., Simoes, P. J. A., Qiu, J., & Fletcher, L. 2015, A&A, 582, A50</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022FrASS...960856K/abstract\">Kerr, G.S. 2022, Front. Astron. Space Sci, Vol. 9</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2009ApJ...699...15N/abstract\">Ning, Z., Cao, W., Huang, J., et al. 2009, ApJ, 699, 15</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...803...84P/abstract\">Polito, V., Reeves, K. K., Del Zanna, G., Golub, L., & Mason, H. E. 2015, ApJ, 803, 84</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...856...34T/abstract\">Tian, H., & Chen, N. H. 2018, ApJ, 856, 34</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023arXiv230811275W/abstract\">Wang, L., Li, Y., Li, Q., Cheng, X., & Ding, M. 2023, arXiv e-prints, arXiv:2308.11275</a>","<a href=\"https://arxiv.org/abs/2309.05745\">Xu et al. 2023, arXiv e-print </a>"],"pubDate":"2023-09-13T01:02:52.043Z"},{"id":"pod_polito_vanessa_2023-08-14T16:50:34.399Z","submitter":"","author":"Vanessa Polito [1,2], Marianne Peterson [3], Lindsay Glesener [3], Paola Testa [4], Sijie Yu [5], Katharine K. Reeves [4], Xudong Sun [6], Jessie Duncan [7]","status":"published","creation-date":"2023-08-14T16:50:34.6Z","last-modified-date":"2023-08-14T19:11:19.286Z","credit":"[1] - Bay Area Environmental Research Institute [2] - Lockheed Martin Solar & Astrophysics Laboratory [3] School of Physics and Astronomy, University of Minnesota Twin Cities - [4] Harvard-Smithsonian Center for Astrophysics - [5] Center for Solar-Terrestrial Research, New Jersey Institute of Technology- [6] Institute for Astronomy, University of Hawaii at Manoa - [7] NASA Goddard Space Flight Center","title":"Multi-wavelength observations and modelling of a microflare: constraining non-thermal particle acceleration","contentBlocks":[{"type":"text","text":"Solar%20flares%20result%20from%20the%20rapid%20release%20of%20large%20amounts%20of%20energy%20via%20the%20magnetic%20reconnection%20process%20in%20the%20solar%20corona.%20Such%20energy%20release%20efficiently%20accelerates%20particles%2C%20heats%20ambient%20plasma%20and%20generates%20magnetohydrodynamic%20%28MHD%29%20waves%20%5Be.g.%20Fletcher%202011%5D.%20An%20increasing%20amount%20of%20evidence%20seems%20to%20suggest%20that%20smaller%20microflare%20or%20even%20nanoflare%20%28even%20fainter%2C%20as-yet%20unresolvable%20events%20predicted%20by%20Parker%20%281988%29%29%20size%20events%20found%20in%20the%20core%20of%20active%20regions%20are%20in%20many%20aspects%20scaled-down%20versions%20of%20large%20flares.%20For%20instance%2C%20IRIS%20observations%20of%20footpoint%20brightenings%20associated%20with%20coronal%20nano-%20to%20microflares%20has%20provided%20new%20indirect%20diagnostics%20of%20the%20presence%20of%20non-thermal%20particles%20in%20small%20heating%20events.%20In%20particular%2C%20IRIS%20observations%2C%20combined%20with%20simulations%2C%20showed%20that%20IRIS%20Si%20IV%20blueshifts%20and%20Mg%20II%20triplet%20enhanced%20emission%20are%20crucial%20signatures%20of%20non-thermal%20particles.%20The%20IRIS%20spectral%20properties%20also%20provide%20valuable%20diagnostics%20of%20the%20properties%20of%20the%20non-thermal%20particles%2C%20such%20as%20the%20low-energy%20cutoff%20%5Cbegin%7Bequation%7D%20E_C%5Cend%7Bequation%7D%20and%20total%20energy%20%5Be.g.%20Testa%20et%20al.%202014%2C%202020%2C%20Polito%20et%20al.%202018%5D."},{"type":"image","file":"","url":"nuggetvideos/2023/08/14/pod_polito_vanessa_2023-08-14T16%3A50%3A34.399Z/aia_iris_overview.jpg","hash":"798389fb669bbf3e7291f58eadcdb41d","mimeType":"image/jpeg","caption":"Figure%201%3A%20B-class%20flare%20on%20April%2029th%202021%20as%20observed%20by%20AIA%20304%20and%2094%20%26Aring%3B%20%28Panels%20a-b%29%2C%2094%20%26Aring%3B%20and%20IRIS%20SJI%201330%20%26Aring%3B%20%28Panel%20c%29.%20The%20IRIS%20field-of-view%20%28FOV%29%20is%20also%20overlaid."},{"type":"text","text":"These%20new%20IRIS%20indirect%20diagnostics%20of%20accelerated%20particles%20in%20small%20events%20are%20interesting%20because%20of%20their%20sensitivity%20to%20small%20events%20which%20are%20typically%20difficult%20to%20observe%20in%20hard%20X-rays%20%28HXRs%29.%20In%20this%20paper%20we%20analyze%20coordinated%20observations%20with%20IRIS%20and%20NuSTAR%20of%20a%20B-class%20flare%20%28Figure%201%29%2C%20which%20provide%20a%20rare%20opportunity%20to%20study%20non-thermal%20particles%20in%20a%20small%20flare%20using%20two%20independent%20diagnostics.%20NuSTAR%20observations%20provide%20a%20direct%20measure%20of%20flare-accelerated%20electrons%2C%20while%20IRIS%20reveals%2C%20with%20great%20sensitivity%2C%20the%20chromospheric%20response%20to%20those%20electrons.%20Hydrodynamic%20modeling%20performed%20using%20the%20RADYN%20code%20%5Be.g.%20Carlsson%20%26amp%3B%20Stein%201997%5D%20connect%20these%20observables."},{"type":"image","file":"","url":"nuggetvideos/2023/08/14/pod_polito_vanessa_2023-08-14T16%3A50%3A34.399Z/multi_map_224.jpg","hash":"c37c1c80204fb64d6b491bcd98873821","mimeType":"image/jpeg","caption":"Figure%202%3A%20Panel%20a%29%3A%20IRIS%20SJI%201330%20%26Aring%3B%20image%20with%20the%20spectrograph%20FOV%20overlaid.%20Panels%20b-e%29%3A%20IRIS%20spectroscopic%20observations%20in%20the%20Si%20IV%20line%20%28intensity%2C%20Doppler%20shift%20velocity%2C%20FWHM%20and%20red-blue%20asymmetry%29.%20Panel%20f%29%3A%20AIA94%20%26Aring%3B%20image%20with%20the%20IRIS%20spectrograph%20FOV%20overlaid.%20Panels%20g-l%29%3A%20IRIS%20spectroscopic%20observations%20in%20the%20Mg%20II%20k%20line%20%28intensity%2C%20peak%20difference%20and%20separation%29%20and%20intensity%20of%20the%20Mg%20II%20triplet%20line.%20The%20cross%20and%20diamond%20symbols%20in%20the%20IRIS%20spectroscopic%20images%20indicates%20a%20position%20where%20we%20observe%20respectively%20blueshifts%20and%20redshifts%20in%20the%20Si%20IV%20line."},{"type":"text","text":"Figure%202%20provides%20an%20overview%20of%20the%20IRIS%20spectral%20observations%20during%20the%20B-class%20flare%20around%2018%3A20%20UT.%20Panels%20a%29%20and%20f%29%20show%20context%20images%20from%20the%20IRIS%20SJI%201330%20%26Aring%3B%20%28showing%20the%20flare%20mini%20ribbon%20observed%20by%20the%20IRIS%20slit%2C%20highlighted%20by%20the%20yellow%20circle%29%20and%20AIA%2094%20%26Aring%3B%20%28showing%20the%20hot%20loops%29%20filters%20respectively%2C%20with%20the%20IRIS%20raster%20FOV%20overlaid.%20Panels%20b%29--e%29%20and%20g%29--l%29%20show%20the%20IRIS%20spectrograph%20data%20in%20the%20same%20FOV.%20In%20particular%2C%20panel%20c%29%20shows%20that%20the%20Si%20IV%20line%20is%20either%20blue%20shifted%20or%20red%20shifted%20in%20the%20mini%20ribbon.%20The%20cross%20and%20diamond%20symbols%20in%20the%20IRIS%20rasters%20indicate%20pixels%20where%20we%20observe%20a%20Si%20IV%20blueshift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0picture%20based%20on%20independent%20measurements%20of%20non-thermal%20particle%20acceleration%20in%20the%20corona%20and%20the%20response%20of%20the%20lower%20atmospheric%20plasma%20to%20the%20non-thermal%20energy%20deposition.%20More%20more%20details%2C%20see%20Polito%20et%20al.%202023."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2011SSRv..159...19F/abstract\">Fletcher, L. et al., Space Science Reviews 159, 1(2011)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1988ApJ...330..474P/abstract\">Parker, E. N., ApJ 330, 474 (1988)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014Sci...346B.315T/abstract\">Testa, P et al. Science,346, 1255724 (2014) </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...889..124T/abstract\">Testa,P., Polito, V. and De Pontieu, ApJ 889, 124 (2020), </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...856..178P/abstract\">Polito, V, Testa, P. et al. ApJ, 856, 178 (2018) </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1992ApJ...397L..59C/abstract\">Carlsson & Stein, ApJ 397, L59(1992)</a>","<a href=\"\">Polito et al. Frontiers in Astronomy and Space Sciences, in press (2023) </a>","","",""],"pubDate":"2023-08-14T19:11:44.557Z"},{"id":"pod_polito_vanessa_2023-05-24T22:27:04.434Z","submitter":"Navdeep K. Panesar (panesar@lmsal.com)","author":"Navdeep K. Panesar[1,2], Sanjiv K. Tiwari[1,2], Ronald L. Moore[3,4], Alphonse C. Sterling[4], and Bart De Pontieu[1,5,6]","status":"published","creation-date":"2023-05-24T22:27:04.462Z","last-modified-date":"2023-06-10T03:24:03.616Z","credit":"[1] Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Bldg. 252, Palo Alto, CA 94304, USA; [2] Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA; [3] Center for Space Plasma and Aeronomic Research (CSPAR), UAH, Huntsville, AL 35805, USA; [4] NASA Marshall Space Flight Center, Huntsville, AL 35812, USA; [5] Rosseland Centre for Solar Physics, University of Oslo, P.O. Box 1029 Blindern, NO0315 Oslo, Norway; [6] Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO0315 Oslo, Norway","title":"Genesis and Coronal-jet-generating Eruption of a Solar Minifilament Captured by IRIS Slit-raster Spectra","contentBlocks":[{"type":"text","text":"We%20report%20observations%20of%20a%20network-edge%20coronal%20hole%20jet%2C%20made%20by%20the%20eruption%20of%20a%20minifilament%2C%20observed%20in%20IRIS%20Mg%20II%20spectra.%20We%20have%20investigated%20the%20properties%20of%20the%20coronal%20jet%20%28including%20the%20formation%20and%20evolution%20of%20the%20pre-jet%20minifilament%2C%20the%20minifilament%20eruption%2C%20and%20the%20jet%20bright%20point%20%28JBP%29%29%20using%20IRIS%20Mg%20II%20k%20spectra%20and%20spectroheliograms%20and%20compare%20these%20with%20simultaneous%20EUV%20observations%20of%20SDO%2FAIA%20%28for%20details%20see%20Panesar%20et%20al%202023%29.%20To%20the%20best%20of%20our%20knowledge%2C%20this%20is%20the%20most%20detailed%20analysis%20so%20far%20of%20an%20on-disk%20minifilament%20eruption%20and%20coronal%20jet%20that%20is%20so%20fully%20captured%20in%20time%20and%20space%20by%20IRIS%20Mg%20II%20spectra%20raster%20scans.%20%0A%0A%0AThe%20IRIS%20slit%20raster%20fully%20covered%20the%20evolution%20of%20the%20minifilament%20and%20jet%20spire.%20Figure%201%20shows%20the%20minifilament%20structure%20and%20the%20jet%20spire.%20The%20minifilament%20shows%20up%20as%20a%20dark%20and%20thick%20structure.%20The%20minifilament%20starts%20to%20rise%20slowly%20at%20about%2020%3A10%20UT.%20Later%2C%20at%20%E2%88%BC20%3A18%20UT%2C%20an%20obvious%20brightening%20%28JBP%20in%20Figure%201%28d%29%29%20starts%20just%20west%20of%20the%20minifilament%20at%20the%20neutral%20line%2C%20before%20the%20start%20of%20the%20jet%20spire%20at%20%E2%88%BC20%3A20%20UT.%20The%20total%20duration%20of%20the%20jet%20spire%20is%2010%20minutes.%20The%20Mg%20II%20minifilament%20appears%20similar%20to%20that%20reported%20by%20Hermans%20%26amp%3B%20Martin%20%281986%29%20and%20Wang%20et%20al.%20%282000%29%20in%20H%CE%B1.%20The%20green%20arrows%20show%20the%20evolution%20of%20the%20minifilament%20activity%20during%20the%20eruption%20phase%20%28Figures%201%28f%E2%80%94h%29%29%2C%20which%20is%20consistent%20with%20the%20spectroheliogram%20video%20%28Panesar%20et%20al%202023%29.%20Further%2C%20the%20time-wavelength%20map%20shows%20a%20strong%20emission%20that%20appears%20at%20the%20location%20of%20the%20jet%20bright%20point%20as%20the%20minifilament%20erupts%20%28Figure%201i%29."},{"type":"image","file":"","url":"nuggetvideos/2023/05/24/pod_polito_vanessa_2023-05-24T22%3A27%3A04.434Z/Fig1.png","hash":"4f74c617c80e72cc7b52cb8184b4851a","mimeType":"image/png","caption":"Figure%201.%20Panels%20%28a%29%E2%80%93%28e%29%20show%20the%20spectroheliograms%20of%20Mg%20II%20k%20line%20at%202796.38%20%26Aring%3B.%20In%20%28b%29%E2%80%93%28e%29%20the%20horizontal%20green%20arrows%20point%20to%20the%20minifilament%20and%20the%20slanted%20green%20arrows%20point%20to%20the%20jet%20spire.%20Panels%20%28f%29%E2%80%93%28i%29%20show%20the%20temporal%20evolution%20of%20the%20spectra%20at%20four%20different%20locations%20marked%20by%20a%20%E2%80%9C%2B%E2%80%9D%20sign%20in%20panel%20%28a%29.%20These%20%E2%80%9C%2B%E2%80%9D%20signs%20are%20taken%20at%20four%20different%20pixels%2C%20along%20the%20IRIS%20slit%2C%20crossing%20the%20jet%20at%20four%20places.%20Panels%20%28f%29%2C%20%28g%29%2C%20%28h%29%2C%20and%20%28i%29%20are%20along%20the%20first%2C%20second%2C%20third%2C%20and%20fourth%20%E2%80%9C%2B%E2%80%9D%20signs%2C%20respectively%20%28from%20left%20to%20right%29.%20The%20green%20arrows%20point%20to%20the%20evolving%20minifilament.%20The%20white%20arrows%20point%20to%20the%20jet%20bright%20point%20%28JBP%29%20jet-base%20brightening.%20In%20panel%20%28a%29%2C%20the%20dotted%20white%20lines%20show%20the%20four%20slit%20positions%20%28labeled%201%E2%80%934%20above%20the%20image%29%20along%20which%20the%20full%20spectra%20of%20the%20Mg%20II%20k%20line%20are%20shown%20in%20Figure%202.%20This%20image%20is%20adapted%20from%20Panesar%20et%20al%202023."},{"type":"text","text":"The%20spectra%20show%20that%20the%20minifilament%20gets%20slightly%20shifted%20toward%20the%20shorter-wavelength%20side%20%28Figures%202%28a2%29%20and%20%28b2%29%29%2C%20which%20means%20that%20the%20minifilament%20plasma%20gets%20blueshifted%20during%20the%20eruption.%20The%20spectra%20shift%20towards%20red%20when%20the%20JBP%20forms%20under%20the%20erupting%20minifilament%20%28Figures%202%28c1%29%20and%20%28d3%29%29.%20This%20redshift%20shows%20that%20there%20are%20downflows%20at%20the%20location%20of%20the%20JBP%2C%20which%20could%20be%20caused%20by%20magnetic%20reconnection%20as%20a%20result%20of%20which%20a%20part%20of%20the%20material%20moves%20up%20and%20some%20move%20down."},{"type":"image","file":"","url":"nuggetvideos/2023/05/24/pod_polito_vanessa_2023-05-24T22%3A27%3A04.434Z/Fig2.png","hash":"79cf651e4677d16f4996b6014375343d","mimeType":"image/png","caption":"Figure%202.%20Progression%20of%20the%20minifilament%20eruption%20in%20IRIS%20spectra%20%28from%20bottom%20to%20top%29.%20Panels%20%28a1%29%E2%80%93%28a3%29%2C%20%28b1%29%E2%80%93%28b3%29%2C%20%28c1%29%E2%80%93%28c3%29%2C%20and%20%28d1%29%E2%80%93%28d3%29%20show%20the%20spectra%20in%20Mg%20II%20k%20line%20along%20the%20four%20slit%20positions%20of%20Figure%201%28a%29%20at%20three%20times.%20Slits%201%2C%202%2C%20and%203%20cross%20the%20minifilament%20and%20the%20jet%20spire%2C%20and%20slit%204%20crosses%20the%20JBP.%20The%20white%20dashed%20boxes%20are%20centered%20on%20the%20minifilament%20and%20JBP.%20In%20%28d1%29%E2%80%93%28d3%29%2C%20the%20center%20of%20the%20JBP%20brightens%20under%20the%20erupting%20minifilament.%20The%20green%20arrows%20%28in%20%28a2%29%20and%20%28b2%29%29%20point%20to%20the%20minifilament%2C%20whereas%20the%20white%20arrows%20%28in%20%28c1%29%20and%20%28d3%29%29%20point%20to%20the%20jet%20bright%20point.%20This%20image%20is%20taken%20from%20Panesar%20et%20al%202023."},{"type":"text","text":"We%20applied%20the%20%5Cbegin%7Bequation%7D%20IRIS%5E%7B2%7D%5Cend%7Bequation%7D%20inversion%20code%20%28Sainz%20Dalda%20et%20al%202019%29%20to%20the%20IRIS%20Mg%20II%20spectra%20to%20map%20the%20thermal%20and%20dynamical%20properties%20of%20the%20minifilament%20eruption%20and%20jet.%20We%20observe%20enhancement%20in%20temperature%20and%20density%20at%20the%20location%20of%20the%20jet%20bright%20point%20under%20the%20rising%20minifilament%20%28Figure%203%29.%20We%20interpret%20that%20the%20increase%20in%20temperature%20and%20density%20is%20due%20to%20the%20reconnection%20brightening%2C%20which%20forms%20underneath%20the%20minifilament.%20The%20inversion%20maps%20show%20a%20downward%20%28redshift%2C%20Figure%203%28b%29%29%20Doppler%20speed%20of%2010%20%5Cbegin%7Bequation%7D%20km%7Es%5E%7B-1%7D%5Cend%7Bequation%7D%2C%20and%20that%20the%20JBP%E2%80%99s%20MgII%20bright%20plasma%20has%20electron%20density%20and%20temperature%20of%20%5Cbegin%7Bequation%7D10%5E%7B12%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%20and%206000%20K%2C%20respectively.%20We%20observe%20upward%20%28Figure%203%28f%29%29%20Doppler%20speeds%20in%20the%20range%20of%205.5%20to%208.5%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B%E2%88%921%7D%5Cend%7Bequation%7D%20with%20an%20uncertainty%20of%20%26plusmn%3B1.5%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B%E2%88%921%7D%5Cend%7Bequation%7D.%20The%20Dopplergram%20also%20shows%20the%20signature%20of%20weak%20redshifts%20%28%281.2%E2%80%932.1%29%20%26plusmn%3B%201.0%20%5Cbegin%7Bequation%7D%20km%7Es%5E%7B-1%7D%5Cend%7Bequation%7D%29%20just%20next%20to%20the%20blueshifts%20%28see%20black%20arrows%20in%20Figure%203%28f%29%29.%20Registration%20of%20the%20Dopplergram%20in%20Figure%203f%29%20with%20the%20Mg%20II%20spectroheliogram%20in%20Figure%203%28h%29%20shows%20that%20the%20two%20opposite%20Doppler%20shifts%20are%20on%20the%20opposite%20edges%20of%20the%20jet%20spire%20seen%20in%20Figure%203%28h%29.%20The%20opposite%20line-of-sight%20velocities%20along%20opposite%20edges%20of%20the%20jet%20spire%20crossed%20by%20the%20IRIS%20slit%20are%20evidence%20that%20the%20jet%20spire%20is%20spinning.%20When%20viewed%20from%20the%20top%2C%20the%20jet%20spire%20is%20spinning%20clockwise%20about%20its%20axis%2C%20consistent%20with%20clockwise%20untwisting%20of%20the%20magnetic%20field%20in%20the%20jet%20spire.%20The%20evidence%20for%20the%20clockwise%20direction%20of%20the%20spire%E2%80%99s%20twist%20is%20that%20when%20viewed%20from%20the%20northwest%2C%20the%20spire%E2%80%99s%20blueshifted%20part%20seen%20in%20the%20IRIS%20Mg%20II%20spectra%20is%20on%20the%20left%20and%20the%20weak%20redshifted%20part%20is%20on%20the%20right."},{"type":"image","file":"","url":"nuggetvideos/2023/05/24/pod_polito_vanessa_2023-05-24T22%3A27%3A04.434Z/Fig3.png","hash":"d5bb7cb5bf7def10eea8b93ca4d7d5b9","mimeType":"image/png","caption":"Figure%203.%20Thermal%20and%20dynamical%20properties%20of%20the%20minifilament%20eruption.%20Panels%20%28a%29%20and%20%28e%29%2C%20%28b%29%20and%20%28f%29%2C%20and%20%28c%29%20and%20%28g%29%20show%20the%20maps%20of%20temperature%2C%20LOS%20velocity%20%28%5Cbegin%7Bequation%7D%20V_%7BLOS%7D%5Cend%7Bequation%7D%29%2C%20and%20electron%20density%20%5Cbegin%7Bequation%7D%20log_%7Bne%7D%5Cend%7Bequation%7D%2C%20respectively%2C%20evaluated%20at%20log%28%CF%84%29%20%3D%20%E2%88%924.2.%20Panels%20%28d%29%20and%20%28h%29%20show%20the%20spectroheliograms%20of%20the%20Mg%20II%20k%20line%20at%202796.38%20%26Aring%3B.%20The%20black%20and%20white%20arrows%20in%20%28a%29%E2%80%93%28c%29%20point%20to%20the%20JBP.%20In%20panel%20%28f%29%20the%20upper%20black%20arrow%20points%20to%20the%20weak%20redshifts%20and%20the%20lower%20arrow%20to%20the%20blueshifts%20along%20the%20jet%20spire.%20This%20image%20is%20taken%20from%20Panesar%20et%20al%202023."},{"type":"text","text":"This%20work%20presents%20the%20first%20detailed%20IRIS%20Mg%20II%20spectroscopic%20analysis%20of%20the%20genesis%20and%20evolution%20of%20an%20on-disk%20pre-jet%20minifilament.%20The%20IRIS%20Mg%20II%20k%20spectra%20and%20spectroheliograms%20show%20%28i%29%20a%20minifilament%20that%20contains%20plasma%20at%20chromospheric%20temperatures%20similar%20to%20H%CE%B1%20filaments%3B%20%28ii%29%20the%20minifilament%20starts%20to%20form%20in%20the%20jet-base%20region%2010%E2%80%9320%20minutes%20before%20the%20jet%20onset%3B%20and%20%28iii%29%20blueshifted%20upflows%20in%20the%20minifilament%E2%80%99s%20plasma%20during%20the%20eruption%20and%20concurrent%20redshifted%20downflow%20at%20the%20JBP%20that%20forms%20underneath%20the%20erupting%20minifilament.%20We%20conclude%20that%20this%20coronal%20jet%20is%20normal%20in%20that%20magnetic%20flux%20cancelation%20builds%20a%20minifilament-carrying%20twisted%20flux%20rope%20and%20triggers%20the%20JBP-generating%20and%20jet-spire-generating%20eruption%20of%20the%20flux%20rope."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...939...25P/abstract\">Panesar N. K., ApJ, 935, 25 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...875L..18S/abstract\">Sainz Dalda., ApJ, 875, 18 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2000ApJ...530.1071W/abstract\">Wang, J., ApJ, 530, 1071 (2000)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1986NASCP2442..369H/abstract\">Hermans, L. M., NASA Conf. Publ. 2442 (1986)</a>","","","","","",""],"pubDate":"2023-06-10T18:21:53.864Z"},{"id":"pod_polito_vanessa_2023-05-01T02:04:24.178Z","submitter":"Momchil Molnar -- mmolnar@ucar.edu (currently at the High Altitude Observatory, NCAR, USA)","author":"Momchil E. Molnar[1, 2, 3*], Kevin P. Reardon[1, 2], Steven R. Cranmer[2, 3], Adam F. Kowalski[1, 2, 3], and Ivan Milic [4,1]","status":"published","creation-date":"2023-05-01T02:04:24.214Z","last-modified-date":"2023-05-11T20:44:25.54Z","credit":"[1] National Solar Observatory, Boulder, Colorado, USA; [2] Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, USA; [3] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA; [4]Astronomical Observatory, Belgrade, Serbia","title":"Constraining the systematics of (acoustic) wave heating estimates in the solar chromosphere","contentBlocks":[{"type":"text","text":"This%20article%20focuses%20on%20constraining%20the%20amount%20of%20acoustic%20wave%20heating%20in%20the%20solar%20chromosphere.%20Acoustic%20wave%20heating%20is%20one%20of%20the%20candidate%20mechanisms%20for%20transport%20of%20the%20missing%20energy%20flux%20required%20to%20maintain%20the%20thermodynamic%20state%20of%20the%20lower%20solar%20atmosphere.%20This%20physical%20mechanism%20has%20been%20discussed%20since%20the%20late%201940s%20%28Biermann%201946%29%2C%20but%20definitive%20conclusions%20for%20its%20importance%20have%20been%20elusive.%20Some%20studies%20suggest%20that%20acoustic%20waves%20play%20a%20significant%20role%20in%20the%20heating%20of%20the%20chromosphere%20%28Abbasvand%20et%20al.%202021%29%2C%20while%20others%20argue%20that%20their%20contribution%20is%20negligible%20compared%20to%20the%20energy%20balance%20needs%20of%20the%20chromospheric%20plasma%20%28Fossum%20and%20Carlsson%202005%29.%20However%2C%20the%20systematic%20differences%20between%20the%20modeling%20approaches%20used%20in%20these%20studies%20are%20not%20well%20constrained.%20The%20main%20goal%20of%20this%20work%20is%20to%20constrain%20the%20systematic%20differences%20of%20acoustic%20wave%20heating%20estimates%20in%20the%20solar%20chromosphere%20by%20combining%20high%20resolution%20solar%20observations%20with%20the%20different%20solar%20modeling%20approaches%20used%20in%20the%20previous%20studies%20%E2%80%93%20ranging%20from%201D%20semi-empirical%20models%20to%20cutting%20edge%203D%20time-dependent%20radiative%20magnetohydrodynamic%20%28rMHD%29%20ones.%20We%20believe%20that%20this%20will%20provide%20a%20better%20foundation%20for%20concluding%20if%20acoustic%20waves%20carry%20%28or%20not%29%20the%20required%20energy%20flux%20to%20heat%20the%20lower%20chromosphere.%20This%20is%20the%20first%20study%20to%20utilize%203D%20time-dependent%20rMHD%20models%20to%20infer%20the%20acoustic%20wave%20flux%20in%20the%20solar%20atmosphere."},{"type":"image","file":"","url":"nuggetvideos/2023/05/01/pod_polito_vanessa_2023-05-01T02%3A04%3A24.178Z/Data_overview_final_png.png","hash":"a73e7d001207395e26e02c867f63830a","mimeType":"image/png","caption":"Figure%201.%20Sit-and-stare%20IRIS%20observations%20of%20a%20quiet%20Sun%20internetwork%20%28left%20column%29%20and%20plage%20region%20%28right%20column%29.%20Panels%20%28a%29%20show%20the%20slitjaw%20images%20in%20the%20279.6%20nm%20filter%2C%20whereas%20panels%20%28b%29%20-%20%28d%29%20show%20the%20relative%20intensity%20and%20Doppler%20velocity%20fluctuations%20in%20time%20along%20the%20slit%20in%20the%20corresponding%20spectral%20diagnostic."},{"type":"text","text":"We%20use%20a%20combination%20of%20high%20resolution%20observational%20data%20from%20IRIS%20%28see%20Figure%201%29%20and%20the%20IBIS%20instrument%20at%20the%20Dunn%20Solar%20Telescope%20%28Cavalini%20et%20al.%202006%29%20in%20this%20study.%20IRIS%20is%20very%20well%20suited%20for%20this%20purpose%20since%20its%20Mg%20II%20h%26amp%3Bk%20spectral%20window%20contains%20multiple%20spectral%20lines%20sampling%20different%20heights%20in%20the%20solar%20atmosphere%20in%20high%20spectral%2C%20spatial%20and%20temporal%20resolution%2C%20as%20seen%20in%20Figure%201.%20On%20the%20modeling%20side%2C%20we%20use%20results%20from%20the%20RADYN%20and%20Bifrost%20codes%2C%20as%20well%20as%20semi-empirical%20FAL%20models.%20We%20created%20synthetic%20diagnostics%20with%20the%20RH15D%20code%20from%20these%20models%20and%20deteriorated%20them%20in%20a%20similar%20fashion%20to%20the%20true%20observations.%20This%20end-to-end%20modeling%20approach%20provides%20us%20with%20a%20connection%20between%20the%20plasma%20parameters%20in%20the%20dynamic%20simulations%20of%20the%20solar%20atmosphere%20and%20the%20actual%20observed%20properties%20of%20the%20spectral%20lines.%20To%20estimate%20the%20acoustic%20wave%20flux%20we%20combine%20the%20amount%20of%20observed%20velocity%20fluctuation%20power%20between%205%20and%2020%20mHz%20in%20different%20spectral%20lines%20with%20the%20plasma%20properties%20inferred%20from%20the%20numerical%20models%2C%20as%20described%20in%20more%20detail%20in%20Molnar%20et%20al.%202023."},{"type":"image","file":"","url":"nuggetvideos/2023/05/01/pod_polito_vanessa_2023-05-01T02%3A04%3A24.178Z/rho_comparison.png","hash":"11cd689c69889fbf18cf001324dd1908","mimeType":"image/png","caption":"Figure%202.%20Plasma%20density%20at%20the%20line%20formation%20height%20for%20the%20Mn%20I%20280.1%20nm%20line%20%28panel%20%28a%29%2C%20lower%20chromosphere%29%20and%20the%20Mg%20II%20k3%20feature%20%28panel%20%28b%29%2C%20upper%20chromosphere%29%20in%20different%20models%20of%20the%20solar%20atmosphere.%20For%20Bifrost%2C%20we%20colored%20the%20points%20in%20the%20enhanced%20network%20patches%20with%20red%2C%20and%20the%20ones%20in%20the%20internetwork%20regions%20in%20blue.%20In%20a%20similar%20fashion%2C%20we%20colored%20the%20FAL%20models%20with%20hotter%20colors%20%28blue%20to%20yellow%29%20for%20correspondingly%20brighter%20%28and%20hotter%29%20emission."},{"type":"text","text":"The%20main%20finding%20of%20this%20study%20is%20that%20the%20highest%20degree%20of%20uncertainty%20introduced%20in%20any%20modeling%20approach%20is%20the%20plasma%20density%20at%20the%20line%20formation%20region.%20As%20we%20show%20in%20the%20Figure%202%2C%20different%20models%20have%20very%20different%20plasma%20density%20at%20the%20formation%20height%20of%20the%20spectral%20lines.%20This%20is%20due%20to%20the%20fact%20that%20the%20line%20formation%20height%20varies%20significantly%20between%20models.%20Furthermore%2C%20there%20is%20a%20significant%20variation%20of%20the%20line%20formation%20plasma%20density%20in%20different%20solar%20features%20in%20the%20same%203D%20model%2C%20which%20also%20vary%20in%20time.%20This%20is%20illustrated%20by%20the%20scatter%20of%20the%20Bifrost%20model%20data%20in%20Figure%202."},{"type":"image","file":"","url":"nuggetvideos/2023/05/01/pod_polito_vanessa_2023-05-01T02%3A04%3A24.178Z/T_coeff_Bifrost_v2.png","hash":"25a1513e3c888049982d7b259f28763b","mimeType":"image/png","caption":"Figure%203.%20Panels%20%28a%29%20and%20%28b%29%3A%20Attenuation%20of%20the%20wave%20amplitudes%20when%20observed%20as%20Doppler%20velocity%20--%20for%20the%20lower%20chromospheric%20diagnostic%20of%20Mn%20I%20280.1%20nm%20line%20%28panel%20a%29%20and%20the%20Mg%20II%20k%20line%20%28panel%20b%29.%20Values%20of%201%20mean%20that%20the%20full%20longitudinal%20amplitude%20of%20the%20wave%20is%20detected%20as%20Doppler%20signal%2C%20whereas%200%20means%20that%20it%20is%20fully%20attenuated.%20Panels%20%28c%29%20-%20%28f%29%3A%20Comparison%20of%20the%20power%20spectra%20of%20the%20velocity%20fluctuations%20in%20the%20solar%20atmosphere%20at%20the%20line%20formation%20heights%20%28dashed%29%20and%20the%20ones%20inferred%20from%20observations%20of%20the%20Doppler%20shifts%20of%20those%20lines%20%28solid%29."},{"type":"text","text":"It%20is%20a%20well%20known%20fact%20that%20the%20observed%20wave%20amplitude%20in%20different%20regions%20of%20the%20solar%20atmosphere%20is%20attenuated%20by%20the%20time%20it%20is%20detected%20as%20Doppler%20velocity%20by%20our%20telescopes%2C%20due%20to%20multiple%20effects%20%28Schmieder%20and%20Mein%201980%2C%20Molnar%20et%20al.%202021%29.%20We%20found%20that%20this%20attenuation%20effect%20has%20a%20strong%20dependence%20on%20the%20solar%20region%20being%20modeled%20in%20the%203D%20simulations%20we%20studied.%20Usually%2C%20we%20expect%20this%20attenuation%20to%20be%20described%20by%20a%20coefficient%20less%20than%20one%2C%20since%20our%20telescopes%20detect%20Doppler%20velocity%20amplitudes%20lesser%20than%20the%20true%20wave%20amplitudes%20in%20the%20solar%20atmosphere.%20However%2C%20in%20the%20hotter%20regions%20of%20the%203D%20simulations%2C%20we%20find%20that%20the%20actual%20vertical%20velocity%20fluctuation%20power%20is%20enhanced%20and%20not%20attenuated.%20This%20effect%20has%20a%20dynamic%20origin%20rooted%20in%20the%20change%20of%20line%20formation%20height%20in%20the%20atmosphere%20and%20cannot%20be%20estimated%20precisely%20by%20using%201D%20semiempirical%20models.%20The%20systematic%20difference%20from%20this%20attenuation%20phenomenon%20is%20that%20using%201D%20%28semi-empirical%29%20models%20leads%20to%20overestimation%20of%20the%20wave%20amplitudes%20and%20the%20wave%20energy%20fluxes."},{"type":"image","file":"","url":"nuggetvideos/2023/05/01/pod_polito_vanessa_2023-05-01T02%3A04%3A24.178Z/acoustic_flux_annotated.png","hash":"18973bca1f03b5f56a32a47508a7bfdf","mimeType":"image/png","caption":"Figure%204.%20Acoustic%20wave%20energy%20flux%20calculated%20from%20IRIS%20and%20IBIS%20observations%20combined%20with%20the%20Bifrost%20models.%20Note%20that%20the%20energy%20requirement%20to%20maintain%20the%20quiet%20and%20plage%20chromosphere%20is%20noted%20by%20the%20solid%20red%20lines.%20The%20amounts%20of%20acoustic%20flux%20in%20the%20Bifrost%20models%20in%20the%20corresponding%20features%20are%20noted%20with%20the%20solid%20lines%20of%20salmon%2Fgreen%20color."},{"type":"text","text":"In%20conclusion%2C%20if%20we%20use%20the%20most%20realistic%20models%20we%20have%20in%20this%20study%20%E2%80%93%20the%203D%20rMHD%20Bifrost%20models%20%E2%80%93%20to%20compute%20the%20acoustic%20wave%20energy%20flux%2C%20the%20result%20is%20that%20acoustic%20waves%20are%20insufficient%20to%20maintain%20the%20low%20chromosphere%20in%20its%20thermodynamic%20state%20%28Molnar%20et%20al.%202023%29%2C%20as%20it%20is%20below%20the%20required%20threshold%20of%20about%204%20kW%2Fm2%20in%20Figure%204%20%28Morosin%20et%20al.%202022%29.%20However%2C%20we%20emphasize%20that%20the%20systematic%20differences%20between%20the%20different%20modeling%20approaches%20is%20significant%20enough%20that%20until%20we%20have%20rMHD%20models%20of%20the%20solar%20atmosphere%20which%20capture%20its%20dynamics%20accurately%20%28Fleck%20et%20al.%202021%29%2C%20these%20conclusions%20will%20be%20severely%20model-%20dependent."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...648A..28A/abstract\">Abbasvand, V., et al. 2021, A&A, 648, A28</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1946NW.....33..118B/abstract\">Biermann, L. 1946, Naturwissenschaften, 33, 118</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2006SoPh..236..415C/abstract\">Cavalini, F. 2006, SoPh, Volume 236, Issue 2, pp.415-439</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021RSPTA.37900170F/abstract\">Fleck, B., et al. 2021, PTRSA, 379, 20200170</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2005Natur.435..919F/abstract\">Fossum, A., & Carlsson, M. 2005, Nature, 435, 919</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021ApJ...920..125M/abstract\">Molnar et al., 2021, ApJ, 920, 125</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023ApJ...945..154M/abstract\">Molnar et al., 2023 ApJ, 945, 154</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022A%26A...664A...8M/abstract\">Morosin et al., A&A, 664, A8 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1980A%26A....84...99S/abstract\">Schmieder, B., & Mein, N. 1980, A&A, 84, 99</a>",""],"pubDate":"2023-05-12T01:13:20.192Z"},{"id":"pod_polito_vanessa_2023-03-29T17:20:30.445Z","submitter":"Rohan Louis (rlouis@prl.res.in)","author":"Rohan E. Louis [1], Shibu K. Mathew [1], Raja Bayanna [1], Christian Beck [2], Debi P. Choudhary [3]","status":"published","creation-date":"2023-03-29T17:20:30.475Z","last-modified-date":"2023-04-13T23:20:45.824Z","credit":"[1] Udaipur Solar Observatory, Physical Research Laboratory Dewali Badi Road, Udaipurâ313001, Rajasthan, India [2] National Solar Observatory (NSO), 3665 Discovery Drive, Boulder, CO 80303, USA [3] Department of Physics and Astronomy, California State University, Northridge (CSUN), CA 91330-8268, USA","title":"Sustained Heating of the Chromosphere and Transition Region Over a Sunspot Light Bridge","contentBlocks":[{"type":"text","text":"The%20solar%20chromosphere%20serves%20as%20an%20important%20conduit%20for%20mass%20and%20energy%20between%20the%20dense%2C%206000%20K%20photosphere%20and%20the%20tenuous%2C%20million%20degree%20corona.%20The%20solar%20chromosphere%20has%20a%20complex%20magnetic%20structure%2C%20where%20the%20plasma%20beta%20changes%20dramatically%20%28Gary%202001%29.%20Determining%20the%20processes%20that%20maintain%20the%20thermal%20structure%20of%20the%20solar%20atmosphere%20is%20one%20of%20the%20fundamental%20problems%20in%20solar%20physics.%20The%20energy%20transfer%20in%20the%20chromosphere%20can%20be%20attributed%20to%20a%20number%20of%20mechanisms%2C%20such%20as%20Alfv%26eacute%3Bn%20waves%20%28Osterbrock%201961%29%2C%20spicules%20%28Beckers%201968%29%2C%20nanoflares%20%28Priest%20et%20al.%202018%29%2C%20magneto-acoustic%20shocks%20%28De%20Pontieu%20et%20al.%202015%29%2C%20and%20%20resistive%20Ohmic%20dissipation%20by%20electric%20currents%20%20%28Parker%201983%2C%20Socas-Navarro%202005%2C%20Louis%20et%20al.%202021%29.%20In%20this%20study%20we%20attempt%20to%20ascertain%20the%20source%20of%20sustained%20heating%20over%20several%20days%20in%20the%20chromosphere%20and%20transition%20region%20above%20a%20sunspot%20light%20bridge%20%28LB%29."},{"type":"image","file":"","url":"nuggetvideos/2023/03/29/pod_polito_vanessa_2023-03-29T17%3A20%3A30.445Z/IRIS-Nugget-fig-01.png","hash":"f009e514f78985df1fd1159a09f3b76","mimeType":"image/png","caption":"Figure%201.%20Top%20panels%3A%20MAST%20Ca%20II%20IR%20line%20core%20image%20%28left%29%20on%202019%20May%2014.%20The%20dashed%20white%20square%20indicates%20a%20smaller%20FOV%20around%20the%20LB%20which%20is%20depicted%20in%20Figure%202.%20The%20middle%20panels%20show%20the%20observed%20and%20synthetic%20spectra%20for%20the%20four%20vertical%20cuts%20in%20the%20line%20core%20image.%20The%20right%20panels%20correspond%20to%20the%20temperature%20stratification%20derived%20from%20the%20NLTE%20inversions%20along%20the%20four%20cuts.%20The%20white%20horizontal%20dashed%20lines%20in%20the%20middle%20and%20right%20panels%20depict%20the%20spectral%20region%20corresponding%20to%20the%20LB%20and%20the%20associated%20temperature%20stratification%2C%20respectively.%20Bottom%20panels%3A%20Same%20as%20above%20but%20for%20the%20IRIS%20Mg%20II%20line."},{"type":"image","file":"","url":"nuggetvideos/2023/03/29/pod_polito_vanessa_2023-03-29T17%3A20%3A30.445Z/IRIS-Nugget-fig-02.png","hash":"e1bc02308108d1864702334ab6ffde8b","mimeType":"image/png","caption":"Figure%202.%20Top%20row%2C%20from%20left%20to%20right%3A%20HMI%20continuum%20intensity%20%28panel%20a%29%2C%20temperature%20derived%20from%20the%20MAST%20Ca%20II%20IR%20line%20%28panels%20b%E2%80%93d%29%2C%20and%20temperature%20derived%20from%20the%20IRIS%20Mg%20II%20line%20%28panels%20e%E2%80%93g%29.%20The%20numbers%20from%20the%20top%20to%20the%20bottom%20row%20below%20the%20temperature%20color%20bar%20represent%20log%20%CF%84%20%3D%20%E2%88%926%2C%20%E2%88%925%2C%20and%20%E2%88%924%2C%20respectively.%20The%20temperature%20color%20bar%20for%20the%20IRIS%20Mg%20II%20line%20is%20similar%2C%20with%20the%20numbers%20in%20the%20parentheses%20corresponding%20to%20the%20observations%20on%202019%20May%2015%20at%2011%3A57%20UT%20for%20the%20maps%20in%20the%20second%20row.%20Second%20row%3A%20the%20same%20as%20above%20on%202019%20May%2015%20at%2011%3A57%20UT.%20Third%20row%3A%20maximum%20line%20intensity%20from%20the%20IRIS%20Mg%20II%20line%2C%20C%20II%20line%2C%20Si%20IV%20line%20%28panels%20h%E2%80%93j%29%2C%20line%20width%20from%20the%20IRIS%20Mg%20II%20line%2C%20C%20II%20line%2C%20Si%20IV%20line%20%28panels%20k%E2%80%93m%29%2C%20and%20AIA%20intensity%20at%20171%26Aring%3B%20%28panel%20n%29%20on%202019%20May%2014.%20Bottom%20row%3A%20the%20same%20as%20above%20on%202019%20May%2015%20at%2011%3A57%20UT.%20The%20black%20contours%20correspond%20to%20the%20HMI%20continuum%20intensity%20and%20outline%20the%20LB."},{"type":"text","text":"We%20combine%20observations%20from%20the%20Multi-Application%20Solar%20Telescope%20%28MAST%29%2C%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%2C%20Hinode%2C%20the%20Atmospheric%20Imaging%20Assembly%20%28AIA%29%2C%20and%20the%20Helioseismic%20and%20Magnetic%20Imager%20%28HMI%29.%20Chromospheric%20temperatures%20were%20retrieved%20from%20the%20MAST%20Ca%20II%20IR%20and%20IRIS%20Mg%20II%20lines%20by%20non-local%20thermodynamic%20equilibrium%20%28NLTE%29%20inversions.%20Line%20widths%2C%20Doppler%20shifts%2C%20and%20intensities%20were%20derived%20from%20the%20IRIS%20lines%20using%20Gaussian%20fits.%20Coronal%20temperatures%20were%20estimated%20through%20the%20differential%20emission%20measure%2C%20while%20the%20coronal%20magnetic%20field%20was%20obtained%20from%20an%20extrapolation%20of%20the%20HMI%20vector%20field.%20%0AAt%20the%20photosphere%2C%20the%20LB%20exhibits%20a%20granular%20morphology%20with%20field%20strengths%20of%20about%20400%20G%20and%20no%20significant%20electric%20currents.%20The%20sunspot%20does%20not%20fragment%2C%20and%20the%20LB%20remains%20stable%20for%20several%20days.%20The%20chromospheric%20temperature%2C%20IRIS%20line%20intensities%20and%20widths%2C%20and%20AIA%20171%20and%20211%20%26Aring%3B%20intensities%20are%20all%20enhanced%20in%20the%20LB%20with%20temperatures%20from%208000%20K%20to%202.5%20MK%20%28Figures%201%2C%202%2C%20and%203%29%20that%20follow%20the%20underlying%20photospheric%20morphology.%20Photospheric%20plasma%20motions%20remain%20small%2C%20while%20the%20chromosphere%20and%20transition%20region%20indicate%20predominantly%20redshifts%20of%205%E2%80%9320%20km%2Fs%20with%20occasional%20supersonic%20downflows%20exceeding%20100%20km%2Fs."},{"type":"image","file":"","url":"nuggetvideos/2023/03/29/pod_polito_vanessa_2023-03-29T17%3A20%3A30.445Z/IRIS-Nugget-fig-04.png","hash":"ae5ea987985f7b91b027b3834a38910","mimeType":"image/png","caption":"Figure%203.%20Photospheric%2C%20chromospheric%2C%20transition%20region%2C%20and%20coronal%20morphology%20in%20and%20around%20NOAA%20AR%2012741%20from%202019%20May%2014%E2%80%9416."},{"type":"text","text":"The%20persistent%20heating%20over%20the%20LB%20is%20counterintuitive%20as%20the%20underlying%20structure%20would%20radiate%20the%20majority%2C%20if%20not%20all%2C%20of%20its%20energy%20once%20having%20evolved%20to%20a%20strongly%20convective%20region%20inside%20the%20sunspot.%20The%20excess%20thermal%20energy%20over%20the%20LB%20is%20about%203.2%20%26times%3B%20%5Cbegin%7Bequation%7D10%5E%7B27%7D%5Cend%7Bequation%7D%20erg%20and%20matches%20the%20radiative%20losses.%20It%20could%20be%20supplied%20by%20magnetic%20flux%20loss%20of%20the%20sunspot%20%287.5%20%26times%3B%20%5Cbegin%7Bequation%7D10%5E%7B27%7D%5Cend%7Bequation%7D%20erg%29%2C%20kinetic%20energy%20from%20the%20increase%20in%20the%20LB%20width%20%284%20%26times%3B%5Cbegin%7Bequation%7D10%5E%7B28%7D%5Cend%7Bequation%7D%20erg%29%2C%20or%20freefall%20of%20mass%20along%20the%20coronal%20loops%20%286.3%20%26times%3B%20%5Cbegin%7Bequation%7D10%5E%7B26%7D%5Cend%7Bequation%7D%20erg%29.%20It%20remains%20an%20open%20question%20whether%20such%20persistent%20heating%20over%20a%20large%20height%20range%20in%20a%20granular%20LB%20is%20indeed%20a%20generic%20phenomenon.%20For%20more%20information%2C%20see%20Loius%20et%20al.%202023."}],"references":["","<a href=\"https://ui.adsabs.harvard.edu/abs/1968SoPh....3..367B/abstract\">Beckers, J. M., Sol. Phys. 3, 367 (1968)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...799L..12D/abstract\">De Pontieu, B. et al., ApJL 799, 12 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2001SoPh..203...71G/abstract\">Gary, G. A., Sol. Phys. 203, 71 (2001)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...652L...4L/abstract\">Louis, R. E. et al., A&A 652L, 4 (2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1961ApJ...134..347O/abstract\">Osterbrock, D. E., ApJ 134, 347 (1961)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1983ApJ...264..635P/abstract\">Parker, E. N., ApJ 264, 635 (1983)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...862L..24P/abstract\">Priest, E. et al., ApJL 862, 24 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2005ApJ...633L..57S/abstract\">Socas-Navarro, ApJL 633, 57 (2005)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2023ApJ...942...62L/abstract\"> Louis et al., ApJ, 942, 62, (2023) </a>"],"pubDate":"2023-04-13T23:21:07.455Z"},{"id":"pod_polito_vanessa_2023-02-23T21:45:14.362Z","submitter":"Vicki Herde (vicki.herde@lasp.colorado.edu)","author":"Vicki L. Herde [1,2] Phillip C. Chamberlin [2] Don Schmit [3] Souvik Bose [4,5,6,7] Adrian Daw [8] Ryan O. Milligan [9] Vanessa Polito [4,5,10]","status":"published","creation-date":"2023-02-23T21:45:14.397Z","last-modified-date":"2023-03-08T17:40:06.319Z","credit":"[1] University of Colorado Boulder, Boulder CO 80303 [2] Laboratory for Atmospheric and Space Physics, 3665 Discovery Dr, Boulder CO 80303 [3] Cooperative Institute for Research in Environmental Sciences, 216 UCB Boulder, CO 80309 [4] Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304, USA [5] Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA [6] Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern 0315, Oslo, Norway [7] Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029, Blindern 0315, Oslo, Norway [8] Solar Physics Laboratory, NASA Goddard Spaceflight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771 [9] Queens University Belfast, University Rd, Belfast BT7 1NN, UK [10] Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, OR 97331","title":"Spicules in IRIS Mg II observations: Automated Identification","contentBlocks":[{"type":"text","text":"In%20this%20paper%20we%20develop%20an%20algorithm%20to%20automatically%20identify%20small%20events%20on%20the%20Sun%20called%20spicules%20using%20exclusively%20observations%20in%20the%20IRIS%20Mg%20II%20emission%20line.%20Spicules%20are%20tiny%20jets%20of%20plasma%20on%20the%20Sun%27s%20surface%20in%20the%20chromosphere%2C%20contained%20within%20small%20magentic%20flux%20tubes.%20They%20are%20visible%20in%20different%20emission%20lines%20at%20different%20points%20in%20their%20evolution%2C%20so%20observing%20spicules%20in%20multiple%20wavelengths%20is%20very%20valuable.%20So%20far%2C%20most%20observations%20have%20happened%20using%20H-alpha%20and%20Ca%20II%20wavelengths%20in%20the%20lower%20chromosphere.%20This%20study%20now%20adds%20the%20ability%20to%20automatically%20identify%20spicules%20in%20Mg%20II%20in%20the%20middle%20chromosphere%20and%20also%20provides%20statistics%20on%20their%20distribution%20and%20duration.%20%20We%20also%20provide%20important%20statistical%20location%20data%20for%20the%20upcoming%20SNIFS%20rocket%20launch%20in%20March%202024.%20The%20SNIFS%20rocket%20observes%20in%20Ly-alpha%20in%20the%20upper%20chromosphere%2C%20and%20Si%20IV%20and%20O%20V%20in%20the%20transition%20region.%20The%20team%20will%20use%20the%20statistics%20learned%20from%20this%20paper%20to%20help%20decide%20where%20the%20rocket%20will%20point%20to%20have%20the%20best%20chance%20of%20observing%20spicules%20during%20its%205-minute%20flight.%20Eventually%2C%20the%20team%20hopes%20to%20be%20able%20to%20combine%20all%20observations%20to%20fully%20characterize%20spicules%20over%20their%20entire%20lifetimes."},{"type":"image","file":"","url":"nuggetvideos/2023/02/23/pod_polito_vanessa_2023-02-23T21%3A45%3A14.362Z/ALL_event_locations_reoccurance.png","hash":"88d2b3520d4a737a4a0297b3fec82872","mimeType":"image/png","caption":"Figure%201.%20Event%20location%20statistics%20for%20the%20active%20region%20%28panels%20a%2Cb%29%2C%20coronal%20hole%20%28panels%20c%2Cd%29%2C%20and%20decayed%20active%20network%20%28panels%20e%2Cf%29%20datasets.%20Left%20column%3A%20Event%20recurrence%20along%20the%20slit%20plotted%20against%20IRIS%20SJI%201400%20image%20for%20context.%20Vertical%20white%20lines%20show%20the%20slit%20location%20while%20variable%20lines%20show%20what%20fraction%20of%20time%20a%20given%20location%20is%20identified%20as%20an%20event.%20Right%20column%3A%20Maps%20of%20event%20identification%20over%20time.%20White%2Fred%20regions%20are%20redshifted%20while%20black%2Fblue%20regions%20are%20blueshifted.%20Each%20plot%20shows%20events%20from%20the%20first%20raster%20position%20over%20time.%20Data%20contaminated%20by%20the%20South%20Atlantic%20Anomaly%20have%20been%20removed%20%28vertical%20white%20strip%20in%20%28d%29%29.%20Events%20underneath%20the%20box%20covering%20Solar%20X%2043%E2%80%9D-53%E2%80%9D%20have%20also%20been%20removed%20from%20this%20paper%E2%80%99s%20statistics%20due%20to%20suspect%20magnetic%20activity."},{"type":"text","text":"To%20identify%20spicule%20spectra%20using%20exclusively%20Mg%20II%20spectral%20profiles%2C%20we%20make%20the%20simplifying%20assumption%20that%20a%20Mg%20II%20h%20spectrum%20can%20be%20modeled%20using%20a%20positive%20emission%20Gaussian%20plus%20a%20negative%20absorption%20Gaussian%20%28Schmit%20et%20al.%202015%29.%20From%20there%2C%20we%20use%20the%20Doppler%20shift%20and%20width%20of%20the%20emission%20Gaussian%20along%20with%20the%20Doppler%20shift%20of%20the%20absorption%20Gaussian%20and%20ratio%20between%20the%20h2%20peaks%20to%20identify%202021%20spicule%20events%20%28Figure%202%29.%20We%20perform%20this%20analysis%20for%20three%20datasets%20spanning%20the%20range%20of%20solar%20magnetic%20environments%3A%20active%20region%2C%20decayed%20active%20region%2C%20and%20coronal%20hole%2C%20using%20both%20sit-and-stare%20observations%20and%20high-cadence%20raster%20observations.%20The%20reduced%20temporal%20coverage%20and%20additional%20spatial%20coverage%20of%20the%20rasters%20do%20not%20meaningfully%20change%20the%20results%20of%20this%20paper."},{"type":"image","file":"","url":"nuggetvideos/2023/02/23/pod_polito_vanessa_2023-02-23T21%3A45%3A14.362Z/official_spicule_example_with_lines_2.png","hash":"cb9bf41f5cba47cf377755f6c18e8824","mimeType":"image/png","caption":"Figure%202.%20Example%20of%20a%20redshifted%20spicule%20under%20the%20IRIS%20slit.%20In%20subplot%20%28a%29%20the%20h1-h3%20labels%20call%20out%20features%20in%20the%20Mg%20II%20line.%20The%20solid%20black%20line%20is%20the%20measured%20spectrum%20while%20the%20blue%20dashed%20line%20is%20a%20reference%20spectrum%2C%20found%20by%20taking%20the%20median%20of%20all%20three%20datasets.%20Subplot%20%28b%29%20highlights%20the%20ways%20a%20spicule%20influences%20the%20Mg%20II%20spectrum%20%28Rouppe%20van%20der%20Voort%20et%20al.%202015%29.%20Parameters%20used%20to%20identify%20this%20spicule%20are%20listed%20in%20the%20top%20right.%20Subplot%20%28c%29%20displays%20the%20positive%20Gaussian%20%28dashed%29%20and%20negative%20Gaussian%20%28dot-dashed%29%20combined%20to%20fit%20a%20Mg%20II%20spectrum%2C%20as%20well%20as%20visually%20displaying%20the%20width%20and%20central%20peak%20locations%20derived%20from%20their%20associated%20Gaussians."},{"type":"text","text":"Figure%201%20displays%20spicule%20detections%20and%20locations%20over%20time%20for%20each%20of%20the%20three%20datasets%2C%20along%20with%20how%20often%20a%20given%20location%20is%20identified%20as%20a%20spicule.%0A%0ABoth%20Type%20I%20and%20Type%20II%20spicules%20are%20identified%20during%20this%20analysis%2C%20with%20Type%20I%20events%20occurring%20more%20often%20in%20the%20active%20region%20dataset.%20This%20analysis%20identifies%20redshift%20and%20blueshift%20events%20with%20a%20fill%20factor%20of%205.7%25%20and%202.2%25%20respectively%20for%20the%20active%20region%20dataset%2C%204.4%25%20and%204.5%25%20for%20the%20coronal%20hole%20dataset%2C%20and%20decreasing%20to%200.79%25%20and%200.59%25%20for%20the%20decayed%20active%20network%20dataset.%20This%20decrease%20in%20event%20identification%20is%20likely%20related%20to%20the%20lack%20of%20absolute%20magnetic%20field%20strengths%20above%2020%20Gauss.%20The%20decayed%20active%20region%20fill%20factor%20is%20about%20half%20the%20factor%20that%20Henriques%20%282016%29%20found%20in%20a%20quiet%20sun%20region%20using%20H-alpha%20observations.%20%0A%0AWhen%20analyzing%20normalized%20event%20rate%20over%20time%2C%20we%20identify%20redshifted%20and%20blueshifted%20events%20in%20an%20active%20region%20at%20a%20rate%20of%200.084%20%5Cbegin%7Bequation%7Darcsec%5E%7B-2%7D%20min%5E%7B-1%7D%5Cend%7Bequation%7D%20and%200.065%20%5Cbegin%7Bequation%7Darcsec%5E%7B-2%7D%20min%5E%7B-1%7D%5Cend%7Bequation%7D%2C%20which%20is%20likely%20an%20undercount.%20This%20is%20comparable%20to%20overall%20rates%20found%20by%20Bose%20%282021%29%2C%20though%20that%20study%20found%20more%20blueshifted%20events%20than%20redshifted%20events.%20%20The%20coronal%20hole%20dataset%20yields%20events%20at%20a%20similar%20rate%20%28though%20skewed%20towards%20blueshifted%29%20which%20is%20likely%20an%20overcount%2C%20while%20the%20decayed%20active%20network%20yields%20a%20much%20lower%20rate.%20%0A%0AWhen%20compared%20to%20magnetic%20field%20strengths%20%28Figure%203%29%2C%20we%20find%20that%200%25-2%25%20of%20locations%20with%20absolute%20magnetic%20field%20strength%20less%20than%2020%20Gauss%20had%20identified%20events%2C%20while%20locations%20with%20absolute%20magnetic%20field%20strengths%2020-200%20Gauss%20were%20identified%20as%20events%202%25-6%25%20of%20the%20time%2C%20with%20active%20region%20event%20identifications%20peaking%20around%204%25%20between%20100-200%20Gauss.%20Coronal%20hole%20events%20appeared%20to%20increase%20steadily%20above%2015%20Gauss%20but%20statistics%20become%20unreliable%20above%2040%20Gauss.%20The%20datasets%20analyzed%20displayed%20few%20magnetic%20field%20strengths%20above%20200%20Gauss%20which%20precludes%20analysis%20at%20stronger%20strengths.%20From%20this%20we%20conclude%20that%20without%20foreknowledge%20of%20spicular%20activity%2C%20a%20mission%20looking%20in%20Mg%20II%20or%20Ly-alpha%20should%20observe%20active%20regions%20with%20field%20strengths%20between%20100-200%20Gauss."},{"type":"image","file":"","url":"nuggetvideos/2023/02/23/pod_polito_vanessa_2023-02-23T21%3A45%3A14.362Z/ALL_mag_fields.png","hash":"1991f02480bfb05868d1bca2927e9ae5","mimeType":"image/png","caption":"Figure%203.%20Event%20occurrences%20with%20relation%20to%20absolute%20magnetic%20field%20strength%20for%20the%20active%20region%20%28a%29%2C%20coronal%20hole%20%28b%29%2C%20and%20decayed%20active%20region%20%28c%29%20datasets.%20The%20thicker%20red%20line%20correspond%20to%20redshifted%20events%20while%20the%20thinner%20blue%20line%20corresponds%20to%20blueshifted%20events.%20Wider%20bins%20indicate%20lower%20B-field%20resolution%20and%20less%20homogeneity.%20The%20final%20bin%20in%20subplot%20%28c%29%20extends%20to%2050%20G%2C%20but%20has%20been%20truncated%20for%20plot%20readability."},{"type":"text","text":"This%20analysis%20struggles%20to%20identify%20the%20most%20extreme%20spicule%20spectra%20for%20which%20one%20emission%20peak%20is%20entirely%20suppressed.%20A%20more%20thorough%20k-means%20clustering%20method%20combined%20with%20H-alpha%20co-observation%20is%20proposed%20to%20supplement%20this%20method.%20%0AIn%20addition%20to%20presenting%20a%20new%20method%20for%20identifying%20spicules%20in%20Mg%20II%20without%20using%20time-dependent%20methods%2C%20this%20analysis%20also%20presents%202021%20spicule%20spectra%20identified%20algorithmically%2C%2024%20of%20which%20are%20shown%20in%20the%20appendix.%20Many%20previous%20examples%20of%20Mg%20II%20spicule%20spectra%20provided%20only%20the%20most%20extreme%20spectral%20examples%2C%20and%20these%20new%20spectra%20may%20be%20used%20to%20examine%20a%20wider%20variety%20of%20Mg%20II%20spicule%20spectral%20shapes.%20For%20more%20details%2C%20see%20Herde%20et%20al.%202023."}],"references":["<a href=\"https://iopscience.iop.org/article/10.1088/0004-637X/811/2/127/meta\">D. Schmit et al., ApJ 811, 127 (2015)</a>","<a href=\"https://iopscience.iop.org/article/10.1088/2041-8205/799/1/L3/meta\">Rouppe van der Voort et al., ApJL 799, L3 (2015)</a>","<a href=\"https://www.aanda.org/articles/aa/abs/2021/03/aa40014-20/aa40014-20.html\">Bose, S. et al, A&A 647, A147 (2021)</a>","<a href=\"https://iopscience.iop.org/article/10.3847/0004-637X/820/2/124/meta\">Henriques V. M. J. et al., ApJ 820, 124 (2016)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022arXiv221204990H/abstract\"> Herde, V., Chamberlin, P. et al. ApJ (in press) (2023) </a>","","","","",""],"pubDate":"2023-03-08T17:40:47.466Z"},{"id":"pod_polito_vanessa_2023-02-01T18:50:43.743Z","submitter":"Kyuhyoun Cho (cho@baeri.org)","author":"Kyuhyoun Cho[1, 2], Paola Testa[3], Bart De Pontieu[2, 4, 5], Vanessa Polito[1, 2, 6]","status":"published","creation-date":"2023-02-01T18:50:43.762Z","last-modified-date":"2023-02-10T20:33:11.423Z","credit":"[1] Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA [2] Lockheed Martin Solar & Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA 94304, USA [3] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02193, USA [4] Rosseland Centre for Solar Physics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo, Norway [5] Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo, Norway [6] Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, OR 97331","title":"A Statistical Study of the IRIS Observational Signatures of Nanoflares and Non-thermal Particles","contentBlocks":[{"type":"text","text":"We%20investigate%20possible%20nanoflare%20signatures%20in%20the%20transition%20region%20and%20chromosphere%20as%20observed%20by%20IRIS%20%28De%20Pontieu%20et%20al.%202014%29.%20If%20the%20nanoflares%20are%20scaled-down%20versions%20of%20large%20flares%2C%20they%20will%20generate%20low-energy%20accelerated%20particles%20and%20appear%20as%20tiny%20small%20spatiotemporal%20brightenings%20in%20the%20lower%20atmosphere.%20Recently%2C%20several%20studies%20investigated%20relevant%20small-scale%20brightenings%20at%20the%20footpoints%20of%20hot%20coronal%20loops%20known%20as%20moss%20region%20from%20high-resolution%20data%20%28Testa%20et%20al.%202014%2C%20Testa%20et%20al.%202020%29%2C%20and%20compared%20their%20spectral%20properties%20with%20the%20results%20of%20numerical%20simulations%20%28Polito%20et%20al.%202018%29.%20Since%20these%20studies%20were%20limited%20to%20a%20dozen%20of%20samples%2C%20we%20greatly%20extended%20the%20number%20of%20brightenings%20using%20an%20automatic%20detection%20algorithm%20based%20on%20AIA%20data%20%28Graham%20et%20al.%202019%29.%0A%0AWe%20found%201082%20small-scale%20brightenings%20in%20four%20active%20regions%20that%20showed%20different%20flaring%20activities.%20The%20Si%20IV%201402%20%26Aring%3B%20and%20Mg%20II%20h%26amp%3Bk%2C%20Mg%20II%20triplet%202798.823%20%26Aring%3B%20lines%20were%20obtained%20from%20IRIS%20sit-and-stare%20observations%2C%20and%20we%20examined%20their%20spatial%2C%20temporal%2C%20environmental%2C%20and%20spectral%20properties%20%28Figure%201%29.%20We%20also%20compared%20the%20observed%20properties%20with%20predictions%20from%20hydrodynamic%20simulations%20using%20the%20RADYN%20code%20%28Carlsson%20%26amp%3B%20Stein%201992%2C%201995%2C%201997a%3B%20Allred%20et%20al.%202015%29%2C%20assuming%20electron%20beam%20heating%20with%20different%20physical%20parameters%20for%20the%20electron%20distribution."},{"type":"image","file":"","url":"nuggetvideos/2023/02/01/pod_polito_vanessa_2023-02-01T18%3A50%3A43.743Z/total_histogram.png","hash":"6b1ff4e7a9ea8e101c23c5df9115edab","mimeType":"image/png","caption":"Figure%201.%20Histograms%20of%20the%20observable%20parameters%20for%20the%20selected%20footpoint%20brightenings%20observed%20by%20IRIS.%20The%20vertical%20dashed%20lines%20indicate%20the%20median%20value%20for%20each%20parameter.%20Each%20color%20of%20the%20histograms%20indicates%20a%20different%20active%20region.%20The%20circle%20and%20cross%20symbols%20in%20the%20histogram%20of%20the%20Si%20IV%20and%20Mg%20II%20spectral%20properties%20represent%20the%20values%20from%20the%20RADYN%20simulations."},{"type":"text","text":"In%20Figure%201%2C%20we%20show%20that%20more%20small-scale%20brightenings%20are%20found%20in%20the%20flare%20productive%20active%20region%20that%20has%20complex%20magnetic%20field%20configuration%20and%20hot%20%28%26gt%3B%204MK%29%20coronal%20plasma.%20The%20observed%20values%20of%20line%20intensities%2C%20Si%20IV%20non-thermal%20velocity%2C%20standard%20deviation%20of%20the%20Doppler%20velocities%2C%20and%20Mg%20II%20triplet%20equivalent%20width%2C%20also%20depend%20on%20the%20level%20of%20activity%20of%20the%20active%20regions.%20We%20found%20that%20the%20occurrence%20of%20Si%20IV%20blueshifts%20and%20Mg%20II%20triplet%20emission%20are%20signatures%20of%20non-thermal%20particles%2C%20in%20agreement%20with%20previous%20findings.%20However%2C%20we%20detected%20a%20larger%20number%20of%20weaker%20events%20than%20in%20the%20previous%20work.%20This%20may%20imply%20that%20smaller%20events%20occur%20more%20frequently.%20%0A%0AIn%20addition%2C%20the%20numerical%20simulations%20reproduce%20well%20the%20spectral%20properties%20of%20small-scale%20brightenings.%20Most%20of%20our%20atmospheric%20models%20reproduce%20similar%20ranges%20of%20values%20for%20the%20spectral%20properties%2C%20with%20the%20exceptions%20of%20the%20Si%20IV%20non-thermal%20velocities%2C%20which%20are%20underestimated%2C%20and%20Mg%20II%20centroid%20Doppler%20velocities%2C%20which%20are%20sometimes%20overestimated%2C%20by%20the%20models.%20The%20observed%20weak%20positive%20relation%20between%20Si%20IV%20Doppler%20velocity%20and%20Mg%20II%20triplet%20emission%20is%20also%20not%20reproduced%20by%20the%20simulations.%20More%20realistic%20models%20are%20required%20to%20solve%20these%20discrepancies."},{"type":"image","file":"","url":"nuggetvideos/2023/02/01/pod_polito_vanessa_2023-02-01T18%3A50%3A43.743Z/Si_IV_anal.png","hash":"cb13b05eff2998ca522144e75407089a","mimeType":"image/png","caption":"Figure%202.%20Joint%20probability%20density%20function%20between%20Si%20IV%20parameters."},{"type":"text","text":"Additionally%2C%20we%20found%20that%20some%20of%20the%20correlations%20between%20different%20spectral%20parameters%20show%20interesting%20features.%20%20For%20example%2C%20the%20Si%20IV%20non-thermal%20velocity%20does%20not%20have%20a%20strong%20correlation%20with%20its%20spectral%20line%20amplitude%20%28Fig%202%29.%20From%20the%20correlation%20with%20Si%20IV%20doppler%20velocity%2C%20it%20can%20be%20inferred%20that%20this%20are%20related%20to%20the%20presence%20of%20multiple%20emission%20components."},{"type":"image","file":"","url":"nuggetvideos/2023/02/01/pod_polito_vanessa_2023-02-01T18%3A50%3A43.743Z/Mg_II_anal.png","hash":"5ed4e540d08b9c9ef9d5bd08e1811f0d","mimeType":"image/png","caption":"Figure%203.%20Joint%20probability%20density%20function%20of%20%28a%29%20Mg%20II%20h%20%26amp%3B%20k%20centroid%20velocities%2C%20%28b%29%20h3%20%26amp%3B%20k3%20velocities%2C%20%28d%29%20h%20centroid%20and%20h3%20velocities.%20%28b%29%20shows%20the%20same%20joint%20probability%20density%20function%20as%20%28a%29%2C%20but%20from%20the%20simulations."},{"type":"text","text":"Further%2C%20the%20Mg%20II%20h%26amp%3Bk%20line%20velocities%20show%20very%20strong%20correlation%20because%20their%20formation%20heights%20are%20considerably%20overlapped%20with%20each%20other%20%28FIg%203%29.%20However%2C%20the%20h%20centroid%20velocity%20and%20h3%20velocity%2C%20which%20indicate%20average%20chromospheric%20and%20upper%20chromospheric%20velocities%20respectively%2C%20show%20poor%20correlation.%20This%20implies%20that%20there%20are%20very%20complex%20chromospheric%20dynamics%20when%20the%20nanoflares%20occur."},{"type":"image","file":"","url":"nuggetvideos/2023/02/01/pod_polito_vanessa_2023-02-01T18%3A50%3A43.743Z/Picture1.png","hash":"6848e764d179a689496da778180529ed","mimeType":"image/png","caption":"Figure%204.%20The%20joint%20probability%20density%20function%20between%20%F0%9D%9C%87%20%3D%20cos%20%F0%9D%9C%83%20and%20Si%20IV%20non-thermal%20velocity."},{"type":"text","text":"Finally%2C%20we%20found%20no%20correlation%20between%20the%20Si%20IV%20non-thermal%20velocity%20and%20inclination%20angle%20%F0%9D%9C%87%3Dcos%20%F0%9D%9C%83%20%28Fig%204%29.%20This%20suggests%20that%20Alfv%26eacute%3Bnic%20waves%20do%20not%20provide%20a%20significant%20contribution%20to%20the%20non-thermal%20velocity%20.%20%0A%0AOur%20study%20helps%20to%20understand%20the%20characteristics%20of%20nanoflares%2C%20and%20contributes%20to%20give%20constraints%20for%20more%20realistic%20numerical%20simulations.%20For%20more%20information%2C%20please%20refer%20to%20Cho%20et%20al.%20%282022%29"}],"references":["<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2015ApJ...809..104A/abstractâÂÂÂÂÂÂ\">Allred, J. C., Kowalski, A. F., & Carlsson, M., ApJ, 809, 104 (2015)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/1992ApJ...397L..59C/abstractâÂÂÂÂÂÂ\">Carlsson, M., & Stein, R. F., ApJL, 397, L59 (1992)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/1995ApJ...440L..29C/abstractâÂÂÂÂÂÂ\">Carlsson, M., & Stein, R. F., ApJL, 440, L29 (1995)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/1997LNP...489..159C/abstractâÂÂÂÂÂÂ\">Carlsson, M., & Stein, R. F., Chromospheric Dynamics - What Can Be Learnt From Numerical Simulations, ed. G. M. Simnett, C. E. Alissandrakis, & L. Vlahos, Vol. 489, 159 (1997) </a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2022arXiv221106832C/abstractâÂÂÂÂÂÂ\">Cho. K., Testa, P., De Pontieu, B., et al., arXiv e-prints, arXiv:2211.05459 (2022)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstractâÂÂÂÂÂÂ\">De Pontieu, B., Title, A. M., Lemen, J. R., et al., SoPh, 289, 2733 (2014)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2019ApJ...880L..12G/abstractâÂÂÂÂÂÂ\">Graham, D. R., De Pontieu, B., & Testa, P., ApJL, 880, L12 (2019)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2018ApJ...856..178P/abstractâÂÂÂÂÂÂ\">Polito, V., Testa, P., Allred, J., et al., ApJ, 856, 178 (2018)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2014Sci...346B.315T/abstractâÂÂÂÂÂÂ\">Testa, P., De Pontieu, B., Allred, J., et al., Science, 346, 1255724 (2014)</a>","<a href=\"âÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2020ApJ...889..124T/abstractâÂÂÂÂÂÂ\">Testa, P., Polito, V., & Pontieu, B. D., ApJ, 889, 124 (2020)</a>"],"pubDate":"2023-02-10T20:33:23.975Z"},{"id":"pod_polito_vanessa_2023-01-03T21:19:17.867Z","submitter":"A. Sainz Dalda (asainz.solarphysics@gmail.com)","author":"A. Sainz Dalda [1,2] and B. De Pontieu [1,3,4]","status":"published","creation-date":"2023-01-03T21:19:17.895Z","last-modified-date":"2023-01-13T19:32:16.073Z","credit":"[1] Lockheed Martin Solar & Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA 94304, USA. [2] Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA. [3] Rosseland Center for Solar Physics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo, Norway. [4] Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo, Norway","title":"Chromospheric Thermodynamic Conditions From Inversions of Complex Mg II h&k Profiles Observed in Flares","contentBlocks":[{"type":"text","text":"We%20have%20investigated%20the%20physical%20conditions%20in%20the%20chromosphere%20during%20the%20maximum%20of%20the%20X-class%20flare%20SOL2014-03-29%2017%3A48UT%20through%20the%20simultaneous%20inversion%20of%20the%20lines%20C%20II%201334%26amp%3B1335%20%26Aring%3B%2C%20the%20Mg%20II%20h%26amp%3Bk%20lines%2C%20and%20the%20Mg%20II%20UV%20triplet%20lines%20observed%20by%20IRIS%20%28De%20Pontieu%20et%20al.%2C%202014%29.%20The%20interpretation%20of%20these%20profiles%20has%20remained%20elusive%2C%20and%2C%20therefore%2C%20the%20physics%20associated%20with%20them%20as%20well.%20The%20main%20characteristic%20of%20these%20profiles%20is%20their%20pointy%20shape.%20By%20using%20the%20inversion%20with%20the%20state-of-the-art%20STiC%20code%20%28de%20la%20Cruz%20et%20al.%202019%29%20on%20the%20representative%20profiles%20%28calculated%20using%20the%20k-means%20technique%29%2C%20we%20have%20obtained%20the%20thermodynamics%20and%20we%20are%20able%20to%20give%20a%20feasible%20explanation%20of%20the%20physical%20conditions%20in%20the%20flare%20ribbons%20%28Sainz%20Dalda%20%26amp%3B%20De%20Pontieu%2C%202022%29."},{"type":"image","file":"","url":"nuggetvideos/2023/01/03/pod_polito_vanessa_2023-01-03T21%3A19%3A17.867Z/figure_1_nugget.png","hash":"d910c3ac3cb5a3eccb741f25937aa868","mimeType":"image/png","caption":"Figure%201.%20Thermodynamics%20of%20the%20X-class%20flare%20SOL2014-03-29%2017%3A48UT%20from%20the%20high%20chromosphere%20%28first%20row%29%20to%20the%20low%20chromosphere%20%28last%20row%29.%20The%20temperature%20%28%5Cbegin%7Bequation%7DT%5Cend%7Bequation%7D%2C%20in%20kK%29%2C%20line-of-sight%20velocity%20%28%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%2C%20in%20km%2Fs%29%2C%20velocity%20of%20turbulent%20motions%20%28%5Cbegin%7Bequation%7Dv_%7Bturb%7D%5Cend%7Bequation%7D%2C%20in%20km%2Fs%29%2C%20and%20electron%20density%20%28log%20%5Cbegin%7Bequation%7Dn_%7Be%7D%5Cend%7Bequation%7D%29%20in%20cm-3%29%20are%20shown%20by%20columns%20%28left%20to%20right%20respectively%29%20at%20different%20optical%20depths%20averaged%20in%20an%20interval%20of%20%CE%94%CF%84%20%3D%20%2B%2F-0.2%20%28in%20rows%29."},{"type":"text","text":"Figure%201%20shows%20the%20thermodynamics%20during%20the%20maximum%20of%20the%20flare%20along%20the%20optical%20depth%2C%20%20log10%28%CF%84500%29.%20That%20is%2C%20the%20reference%20of%20the%20optical%20depth%20unity%20corresponds%20to%20the%20continuum%20at%20500%20nm.%20For%20the%20sake%20of%20simplicity%20in%20the%20notation%2C%20we%20use%20log%28%CF%84%29.%20As%20a%20rough%20reference%2C%20%0Awe%20consider%20the%20high%20chromosphere%20in%20the%20optical%20depth%20range%20%E2%88%926.5%20%26lt%3B%20log%28%CF%84%29%26lt%3B%20%E2%88%925%2C%20the%20mid%20chromosphere%20in%20%E2%88%925%20%26lt%3B%20log%28%CF%84%29%26lt%3B%20%E2%88%924%2C%20the%20low%20chromosphere%20in%20%E2%88%924%20%26lt%3B%20log%28%CF%84%29%26lt%3B%20%E2%88%922%2C%20and%20the%20high%20photosphere%20in%20%E2%88%922%20%26lt%3B%20log%28%CF%84%29%26lt%3B%20%E2%88%921.%20Although%20Figure%201%20shows%20a%20moment%20in%20the%20flare%20evolution%2C%20the%20different%20parts%20of%20the%20ribbon%20%28leading%20and%20trailing%20edges%29%20may%20be%20at%20different%20thermodynamic%20stages%20as%20the%20energy%20is%20propagating%20through%20the%20ribbon.%20Thus%2C%20in%20the%20high%20chromosphere%20%28first%20row%29%2C%20the%20temperature%20in%20the%20trailing%20edge%20of%20the%20lower%20ribbon%20%E2%80%94%20located%20at%20%5BX%2CY%5D%20%3D%20%5B517%20%E2%88%92%20526%2C%20263%5D%20%E2%80%94%20has%20a%20higher%20temperature%20%20than%20in%20the%20rest%20of%20the%20ribbon.%20That%20means%2C%20the%20trailing%20edge%20has%20been%20energized%20longer%20than%20the%20leading%20edge.%20In%20addition%2C%20in%20the%20trailing%20edge%20the%20temperature%20in%20the%20high%20chromosphere%20is%20higher%20than%20in%20the%20mid%20chromosphere.%20However%2C%20the%20inner%20part%20of%20the%20ribbon%20and%20the%20leading%20ribbon%2C%20%20the%20temperature%20in%20the%20high%20chromosphere%20%28first%20row%29%20is%20lower%20than%20in%20the%20mid%20chromosphere%20%28second%20row%20of%20Figure%201%29.%20These%20observations%20support%20a%20scenario%20in%20which%20energy%20is%20deposited%20in%20the%20middle%20chromosphere%2C%20with%20an%20associated%20local%20temperature%20increase.%20This%20energy%20deposition%20affects%20the%20high%20chromosphere%20at%20later%20times%20in%20the%20inner%20ribbon%20and%20the%20leading%20ribbon%2C%20as%20the%20flare%20evolves%2C%20but%20it%20has%20already%20affected%20to%20the%20trailing%20edge.%20Allred%20et%20al.%20%282015%29%20obtained%20a%20similar%20behavior%20in%20numerical%20models%20of%20flares%20energy%20deposition%20in%20the%20chromosphere.%0A%0AThe%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20in%20the%20ribbon%20shows%20a%20divergent%20behavior%20in%20the%20high-%20and%20mid-chromosphere%20%28first%20and%20second%20row%20respectively%20in%20the%20second%20column%20of%20Figure%201%29.%20Thus%2C%20we%20observe%20predominantly%20an%20upflow%20in%20the%20high%20chromosphere%20%28log%28%CF%84%29%3D%20%E2%88%925.8%29%2C%20while%20in%20the%20middle%20chromosphere%20and%20lower%20regions%20in%20the%20atmosphere%20%28%E2%88%924.2%20%26lt%3B%20log%28%CF%84%29%29%20we%20observe%20a%20downflow.%20This%20divergent%20flow%20is%20compatible%20with%20a%20scenario%20where%20an%20electron%20beam%20propagating%20downwards%20from%20the%20flare%20reconnection%20site%20in%20the%20corona%20impacts%20the%20dense%20chromosphere%20%28thick%20target%20model%29.%20Such%20divergent%20flows%20have%20also%20been%20obtained%20in%20radiation%20hydrodynamic%20experiments%20by%20Kerr%20et%20al.%202016%20and%20Kowalski%20et%20al.%202017.%20This%20divergent%20region%20is%20observed%20also%20in%20the%20leading%20edge%20in%20the%20low-chromosphere%20and%20high-chromosphere%2C%20making%20this%20scenario%20compatible%20with%20the%20results%20obtained%20by%20Graham%20et%20al.%202020%20and%20the%20one%20previously%20suggested%20by%20Libbrecht%20et%20al.%202019.%20Again%2C%20different%20parts%20of%20the%20ribbon%20are%20simultaneously%20experiencing%20different%20physical%20conditions."},{"type":"image","file":"","url":"nuggetvideos/2023/01/03/pod_polito_vanessa_2023-01-03T21%3A19%3A17.867Z/figure_2_nugget.png","hash":"9bf89573e12721e71134b7e468ea498d","mimeType":"image/png","caption":"Figure%202.%20Example%20of%20an%20extremely%20pointy%20profile.%20From%20top%20to%20bottom%2C%20from%20left%20to%20right%3A%20C%20II%201334%20%26amp%3B%201335%20%28panel%20A%29%2C%20Mg%20II%20UV1%20%28B%29%2C%20Mg%20II%20h%26amp%3Bk%20%28C%20and%20left%20and%20right%20sub-panels%20in%20panel%20C%29%2C%20and%20Mg%20II%20UV2%26amp%3B3%20%28C%20and%20center%20sub-panel%20in%20panel%20C%29%20lines.%20The%20observed%20profile%20is%20display%20in%20dotted%2C%20black%20line.%20The%20dashed%2C%20blue%20line%20corresponds%20to%20the%20inversion%20only%20taking%20into%20account%20the%20Mg%20II%20h%26amp%3Bk%20lines.%20The%20fuchsia%20line%20corresponds%20to%20the%20inversion%20considering%20simultaneously%20the%20C%20II%201334%20%26amp%3B%201335%20.%20lines%2C%20the%20Mg%20II%20UV1%20line%2C%20and%20the%20Mg%20II%20h%26amp%3Bk%20lines%20-%20including%20the%20Mg%20II%20UV2%26amp%3B3%20lines.%20The%20last%20row%20shows%20the%20model%20recovered%20from%20the%20inversion%3A%20temperature%20%28%5Cbegin%7Bequation%7DT%5Cend%7Bequation%7D%2C%20in%20orange%29%2C%20logarithm%20of%20the%20electron%20density%20%28%5Cbegin%7Bequation%7Dn_%7Be%7D%5Cend%7Bequation%7D%2C%20in%20blue%29%2C%20velocity%20of%20turbulent%20motions%20or%20micro-turbulence%20%28%5Cbegin%7Bequation%7Dv_%7Bturb%7D%5Cend%7Bequation%7D%2C%20in%20green%29%2C%20and%20line-of-sight%20velocity%20%28%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%2C%20in%20violet%29.%20The%20dashed%20lines%20correspond%20to%20the%20model%20recovered%20from%20the%20inversion%20considering%20only%20the%20Mg%20II%20h%26amp%3Bk%20lines%2C%20while%20the%20solid%20lines%20correspond%20to%20the%20inversion%20considering%20all%20the%20spectral%20lines%20mentioned%20above.%20The%20red%20shade%20area%20in%20the%20model%20atmosphere%20panels%20%28D%20and%20E%29%20indicates%20the%20optical%20depth%20range%20that%20we%20should%20not%20consider%20as%20reliable."},{"type":"text","text":"These%20thermodynamic%20values%20have%20been%20obtained%20by%20the%20simultaneous%20inversion%20of%20the%20spectral%20lines%20mentioned%20above%2C%20that%20gives%20us%20an%20unprecedented%20coverage%20from%20the%20top%20of%20the%20chromosphere%20to%20the%20top%20of%20the%20photosphere.%20The%20Mg%20II%20h%26amp%3Bk%20spectral%20lines%20in%20the%20ribbon%20during%20the%20maximum%20of%20the%20flare%20are%20either%20extremely%20pointy%20profiles%20or%20combined%20pointy%20profiles.%20Figure%202%20shows%20an%20example%20of%20an%20extremely%20pointy%20profile%20%28in%20dotted%20line%29%2C%20the%20inverted%20profile%20%28best%20fit%20to%20the%20observed%20one%2C%20in%20fuchsia%29%2C%20and%20the%20thermodynamic%20parameters%20%28in%20the%20last%20row%29.%20These%20profiles%20are%20associated%20with%20strong%20gradients%20in%20the%20mid-%20and%20high-chromosphere%2C%20showing%20divergent%20flows%20in%20some%20instances.%20Figure%203%20shows%20an%20example%20of%20a%20combined%20pointy%20profile.%20In%20this%20case%2C%20we%20can%20observe%20the%20behavior%20mentioned%20above%3A%20a%20high%20temperature%20at%20log%28%CF%84%20%29%3D%20%E2%88%925.8%2C%20%20followed%20by%20a%20lower%20temperature%20in%20the%20high-chromosphere%20%28%28log%28%CF%84%20%29%3D%20%E2%88%926.4%29%2C%20i.e.%20the%20high-chromosphere%20has%20not%20been%20yet%20energized%20from%20the%20mid-chromosphere.%20The%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20shows%20a%20divergent%20flow%20in%20the%20low%20chromosphere%2C%20at%20log%28%CF%84%29%3D%20%E2%88%923.8."},{"type":"image","file":"","url":"nuggetvideos/2023/01/03/pod_polito_vanessa_2023-01-03T21%3A19%3A17.867Z/figure_3_nugget.png","hash":"b80371df029474810250bb3ad1c34ab5","mimeType":"image/png","caption":"Figure%203.%20Similar%20to%20Figure%202%20for%20a%20combined%20pointy%20profile."},{"type":"text","text":"Two%20key%20aspects%20of%20this%20investigation%20have%20been%20to%20understand%20what%20conditions%20may%20lead%20to%20the%20extremely%20pointy%20profiles%2C%20and%20at%20what%20optical%20range%20the%20thermodynamic%20recovered%20from%20the%20inversion%20is%20feasible.%20Figure%204%20shows%20how%20an%20extremely%20pointy%20profile%20can%20be%20obtained%20by%20considering%20a%20strong%20gradient%20in%20the%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20in%20the%20high%20chromosphere.%20On%20one%20hand%2C%20by%20using%20the%20response%20functions%2C%20and%20on%20the%20other%20hand%2C%20by%20decomposing%20the%20role%20played%20by%20the%20thermodynamic%20parameters%20independently%2C%20we%20have%20verified%20that%20we%20can%20trust%20the%20values%20obtained%20from%20-6.5%20%26lt%3B%20log%28%CF%84%29%20%26lt%3B%20%E2%88%922.2%2C%20be%20cautious%20between%20-2.2%20%26lt%3B%20log%28%CF%84%29%20%26lt%3B%20%E2%88%921.8%2C%20and%20ignore%20them%20below%20-1.8%20%26lt%3B%20log%28%CF%84%29.%20More%20details%20in%20Sainz%20Dalda%20%26amp%3B%20De%20Pontieu%2C%202022."},{"type":"image","file":"","url":"nuggetvideos/2023/01/03/pod_polito_vanessa_2023-01-03T21%3A19%3A17.867Z/figure_4_nugget.png","hash":"aef27def515df325bd6be2e3932e35a","mimeType":"image/png","caption":"Figure%204.%20Creating%20an%20Mg%20II%20h%26amp%3Bk%20extremely%20pointy%20profile%20%28red%20or%20blue%2C%20in%20panels%20A%20to%20C%29%20from%20a%20double-peaked%20Mg%20II%20h%26amp%3Bk%20profile%20%28grey%29%20by%20considering%20an%20extreme%20gradient%20downflow%20%28red%29%20or%20upflow%20%28blue%29%20in%20the%20high%20chromosphere%20%28panel%20G%29.%20The%20grey%20lines%20in%20the%20model%20parameters%20correspond%20to%20the%20grey%20spectra.%20The%20extremely%20pointy%20profile%20red%20%28blue%29%20corresponds%20to%20a%20model%20atmosphere%20with%20the%20same%20temperature%2C%20%5Cbegin%7Bequation%7Dv_%7Bturb%7D%5Cend%7Bequation%7D%2C%20%5Cbegin%7Bequation%7Dn_%7Be%7D%5Cend%7Bequation%7D%2C%20but%20a%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20with%20a%20strong%20downflow%20%28upflow%29%20displayed%20in%20red%20%28blue%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...809..104A\"> Allred, Kowalski, & Carlsson, The Astrophysical Journal, 809, 104 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019A&A...623A..74D\"> de la Cruz Rodríguez et al., Astronomy and Astrophysics, 623, A74 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D\"> De Pontieu et al., Solar Physics, 289, 2733 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...895....6G\"> Graham et al., The Astrophysical Journal, 895, 6 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...827..101K\"> Kerr et al., The Astrophysical Journal, 827, 101 (2016)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...836...12K\"> Kowalski et al., The Astrophysical Journal, 836, 12 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019A&A...621A..35L\"> Libbrecht et al., Astronomy and Astrophysics, 621, A35 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022arXiv221105459S\"> Sainz Dalda & De Pontieu, arXiv e-prints, arXiv:2211.05459 (2022)</a>","",""],"pubDate":"2023-01-13T19:32:51.666Z"},{"id":"pod_polito_vanessa_2022-12-01T18:14:47.974Z","submitter":"Huidong Hu","author":"Huidong Hu[1], Ying D. Liu[1], Lakshmi Pradeep Chitta[2], Hardi Peter[2], and Mingde Ding[3]","status":"published","creation-date":"2022-12-01T18:14:48.003Z","last-modified-date":"2022-12-09T18:53:32.05Z","credit":"[1] National Space Science Center, Chinese Academy of Sciences, China. [2] Max Planck Institute for Solar System Research, Germany. [3] School of Astronomy and Space Science, Nanjing University, China.","title":"Spectroscopic and Imaging Observations of Spatially Extended Magnetic Reconnection in the Splitting of a Solar Filament Structure","contentBlocks":[{"type":"text","text":"One%20indicator%20of%20magnetic%20reconnection%20is%20the%20Doppler%20effect%20of%20the%20reconnection%20outflows.%20Previous%20work%20has%20shown%20that%20blue-%20and%20redshifts%20of%20bidirectional%20reconnection%20outflows%20are%20commonly%20observed%20in%20confined%20regions%20on%20the%20Sun%20%28e.g.%2C%20Chifor%20et%20al.%202008%3B%20Tian%20etal.2018%3B%20Ortiz%20et%20al.%202020%29.%20Spatially%20resolved%20spectroscopic%20observations%20covering%20extended%20regions%20in%20the%20solar%20atmosphere%20are%20rare%2C%20and%20thus%20the%20distribution%20of%20reconnection%20outflows%20and%20thermal%20properties%20on%20the%20Sun%20is%20unclear.%0A%0AModels%20and%20imaging%20observations%20suggest%20that%20magnetic%20reconnection%20can%20occur%20internally%20in%20a%20filament%20structure%20and%20is%20associated%20with%20the%20splitting%20and%2For%20partial%20eruption%20of%20the%20filament%20structure%20%28e.g.%2C%20Gilbert%20et%20al.%202001%3B%20Gibson%20%26amp%3B%20Fan%202006%3B%20Tripathi%20et%20al.%202009%3B%20Liu%20et%20al.%202012%29.%20However%2C%20Doppler%20shifts%20of%20bidirectional%20outflows%2C%20as%20definite%20evidence%20for%20reconnection%20in%20solar%20filament%20splitting%2C%20have%20not%20been%20detected%20so%20far.%0A%0AIn%20Hu%20et%20al.%20%282022%29%2C%20we%20report%20a%20magnetic-reconnection%20event%20that%20causes%20the%20splitting%20of%20a%20solar%20filament%20structure%2C%20based%20on%20spatially%20resolved%20spectroscopic%20data%20from%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%20and%20images%20from%20the%20Solar%20Dynamics%20Observatory%20%28SDO%2C%20Pesnell%20et%20al.%202012%29.%0A%0AA%20filament%20structure%20in%20Active%20Region%2012665%20was%20split%20into%20two%20upper%20and%20lower%20branches%20by%20magnetic%20reconnection.%20It%20eventually%20erupted%20partially%2C%20with%20the%20upper%20branch%20ejected%20and%20the%20lower%20branch%20retained.%20The%20evolution%20of%20the%20filament%20structure%20is%20illustrated%20in%20Figure%201%20of%20Hu%20et%20al.%20%282022%29%20and%20in%20animation%20at%20https%3A%2F%2Fyoutu.be%2FaFNowNmP0tQ%20.%20The%20splitting%20by%20reconnection%20was%20captured%20on%20a%20rare%20occasion%20with%20a%20spatially%20resolved%20IRIS%20raster%20scan.%0A%0AFigure%201%20shows%20the%20Doppler%20velocity%2C%20nonthermal%20width%2C%20and%20intensity%20derived%20from%20a%20single%20Gaussian%20fit%20of%20Si%20IV%201393.755%20%26Aring%3B%20line%20profiles%20in%20the%20IRIS%20data.%20Neighboring%20large%20blue-%20and%20redshifts%20of%20%E2%89%B350%20km%2Fs%20in%20the%20brightening%20region%20of%20304%20%26Aring%3B%20between%20the%20two%20filament%20branches%20are%20revealed%2C%20which%20spatially%20correspond%20to%20large%20nonthermal%20widths%20and%20enhanced%20intensities%20%28brightening%29%20of%20the%20Si%20IV%20line.%20These%20are%20the%20signature%20of%20magnetic%20reconnection%2C%20after%20which%20the%20filament%20structure%20is%20split%20into%20two%20branches.%20The%20length%20of%20the%20reconnection%20region%20is%20unprecedentedly%20%7E20%26quot%3B%20%28no%20less%20than%2014%20000%20km%3B%20the%20distance%20between%20the%20two%20crosses%20%28%26quot%3B%2B%26quot%3B%29%20in%20Figure%201%28e%29%29."},{"type":"image","file":"","url":"nuggetvideos/2022/12/01/pod_polito_vanessa_2022-12-01T18%3A14%3A47.974Z/fig2.png","hash":"c554cbb8bf38fc9fac914b5e7a446b86","mimeType":"image/png","caption":"Figure%201.%20Magnetic%20reconnection%20in%20the%20filament%20splitting%20observed%20with%20SDO%20and%20IRIS.%20In%20%28a%29%20the%20rectangle%20denotes%20the%20field%20of%20view%20of%20the%20IRIS%20scan%3B%20%26quot%3BF1%26quot%3B%2C%20%26quot%3BF2%26quot%3B%2C%20and%20the%20arrows%20indicate%20the%20lower%20and%20upper%20filament%20branches.%20In%20%28c%29%20the%20two%20cyan%20slits%20%26quot%3BS1%26quot%3B%20and%20%26quot%3BS2%26quot%3B%20mark%20where%20the%20spectra%20are%20displayed%20in%20Figure%202%28a%29%E2%80%93%28b%29%3B%20the%20black%20dashes%20denote%20where%20on%20the%20slits%20the%20line%20profiles%20are%20plotted%20in%20Figure%202%28c%29%E2%80%93%28d%29."},{"type":"text","text":"As%20displayed%20in%20Figure%202%2C%20blue-%20and%20redshifts%20of%20the%20upward%20and%20downward%20outflows%20are%20detected%20on%20slits%20marked%20in%20Figure%201%28c%29.%20The%20reduction%20of%20the%20overall%20line%20width%20indicates%20that%20the%20line-of-sight%20velocities%20decrease%20remarkably%20after%20the%20bidirectional%20outflows%20have%20left%20the%20reconnection%20site.%20A%20double%20Gaussian%20fit%20of%20the%20profiles%20reveals%20that%20the%20outflow%20velocity%20is%20up%20to%20%7E150%20km%2Fs.%20We%20can%20also%20see%20line%20broadening%20on%20the%20blue%20wing%2C%20at%20%26quot%3BS1-iv%26quot%3B%20and%20%26quot%3BS2-iv%26quot%3B%2C%20several%20arcseconds%20away%20from%20the%20reconnection%20site%2C%20which%20may%20be%20an%20indicator%20of%20turbulence%20that%20is%20induced%20when%20the%20upward%20outflow%20interacts%20with%20the%20upper%20filament%20branch."},{"type":"image","file":"","url":"nuggetvideos/2022/12/01/pod_polito_vanessa_2022-12-01T18%3A14%3A47.974Z/fig3.png","hash":"552b3817151a9550c3fec5183ab884ee","mimeType":"image/png","caption":"Figure%202.%20Spectra%20of%20the%20bidirectional%20outflows%20from%20the%20reconnection%20site%20at%20positions%20defined%20in%20Figure%201%28c%29.%20In%20%28c%29%E2%80%93%28d%29%2C%20the%20black%20curves%20are%20the%20observed%20profiles%3B%20the%20cyan%20curves%20represent%20the%20total%20fits%3B%20and%20the%20red%20and%20blue%20curves%20plot%20the%20two%20Gaussian%20components."},{"type":"text","text":"Figure%203%20presents%20the%20differential-emission-measure%20%28DEM%29%20analysis%20of%20the%20reconnection%20region.%20The%20DEM%20analysis%20shows%20that%20the%20temperature%20during%20the%20reconnection%20is%20%7E14%20MK%2C%20%7E9%20MK%20higher%20than%20that%20before%20the%20reconnection.%20The%20electron%20density%20is%20%5Cbegin%7Bequation%7D%20%5Csim%203.9%20%5Ctimes%2010%5E%7B10%7D%5C%20%5Cmathrm%7Bcm%7D%5E%7B-3%7D%20%5Cend%7Bequation%7D%2C%20about%20twice%20that%20before%20the%20reconnection.%20By%20assuming%20a%20volume%20size%2C%20the%20total%20thermal%20energy%20is%20estimated%20to%20be%20%5Cbegin%7Bequation%7D%20%5Csim%201.3%20%5Ctimes%2010%5E%7B27%7D%20%5Cend%7Bequation%7D%20ergs%2C%20which%20is%20about%20ten%20times%20the%20kinetic%20energy."},{"type":"image","file":"","url":"nuggetvideos/2022/12/01/pod_polito_vanessa_2022-12-01T18%3A14%3A47.974Z/fig4.png","hash":"d02381d36c7da2cbe9ca7abed19cae3b","mimeType":"image/png","caption":"Figure%203.%20Differential%20emission%20measure%20%28DEM%29%20and%20emission%20measure%20%28EM%29%20of%20the%20reconnection%20region%20based%20on%20SDO%2FAIA%20observations.%20The%20temporal%20DEM%20in%20%28c%29%20is%20averaged%20over%20the%20four%20pixels%20specified%20by%20the%20square%20in%20%28b%29."},{"type":"text","text":"We%20have%20provided%20spectroscopic%20evidence%20for%20the%20splitting%20of%20a%20filament%20structure%20by%20magnetic%20reconnection.%20The%20reconnection%20is%20in%20an%20extended%20region%20with%20an%20unprecedented%20length.%20The%20thermal%20energy%20overwhelmingly%20dominates%20the%20kinetic%20energy%20in%20this%20reconnection%20event.%0A%0AFor%20details%2C%20please%20see%20Hu%20et%20al.%20%282022%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2001ApJ...549.1221G/abstract\">Gilbert, H. R., et al. ApJ 549.2 (2001): 1221.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2006ApJ...637L..65G/abstract\">Gibson, S. E., and Y. Fan. ApJL 637.1 (2006): L65.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2008A%26A...481L..57C/abstract\">Chifor, C., et al. A&A 481.1 (2008): L57-L60.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2009A%26A...498..295T/abstract\">Tripathi, D., et al. A&A 498.1 (2009): 295-305.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2012ApJ...756...59L/abstract\">Liu, R., et al. ApJ 756.1 (2012): 59.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2012SoPh..275....3P/abstract\">Pesnell, W. D., et al. SoPh 275.1 (2012): 3-15.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu, B., et al. SoPh 289.7 (2014): 2733-2779.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...854..174T/abstract\">Tian, H., et al. ApJ 854.2 (2018): 174.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...633A..58O/abstract\">Ortiz, A., et al. A&A 633 (2020): A58.</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...940L..12H/abstract\">Hu, H., et al. ApJL 940.1 (2022): L12.</a>"],"pubDate":"2022-12-09T18:53:37.592Z"},{"id":"pod_polito_vanessa_2022-10-25T17:48:34.066Z","submitter":"Dr. Yamini K. Rao","author":"Yamini K. Rao, Giulio Del Zanna, Helen E. Mason, and Roger Dufresne","status":"published","creation-date":"2022-10-25T17:48:34.071Z","last-modified-date":"2022-11-15T18:54:50.799Z","credit":"DAMTP, University of Cambridge, Wilberforce Rd, Cambridge CB3 0WA, United Kingdom","title":"Path length studies in the solar transition region using IRIS","contentBlocks":[{"type":"text","text":"Mass%20and%20energy%20are%20transferred%20from%20the%20lower%20atmosphere%20to%20the%20corona%20through%20the%20transition%20region.%20An%20understanding%20of%20the%20dynamical%20processes%20in%20the%20transition%20region%20could%20be%20complemented%20by%20studies%20about%20path%20lengths%20and%20filling%20factors%20%28Del%20Zanna%20and%20Mason%2C%202018%29.%20The%20path%20lengths%2C%20%20%5Cbegin%7Bequation%7Ddh%5Cend%7Bequation%7D%2C%20are%20generally%20obtained%20from%20intensities%20and%20densities%20measured%20from%20spectral%20lines%20and%20can%20be%20approximated%20by%20the%20following%20formula%3A%0A%0A%5Cbegin%7Bequation%7D%0AI%3DG%28T%29N_e%5E2dh%0A%5Cend%7Bequation%7D%0A%0Awhere%20%5Cbegin%7Bequation%7DG%28T%29%5Cend%7Bequation%7D%20is%20the%20peak%20value%20of%20the%20contribution%20function%2C%20%5Cbegin%7Bequation%7DN_e%5Cend%7Bequation%7D%20is%20the%20electron%20density%2C%20and%20%5Cbegin%7Bequation%7Ddh%5Cend%7Bequation%7D%20is%20the%20path%20length.%20The%20path%20lengths%20give%20a%20line-of-sight%20measure%20of%20the%20thickness%20of%20the%20transition%20region%20plasma%20at%20%5Cbegin%7Bequation%7D10%5E5%5Cend%7Bequation%7D%20K.%20In%20our%20present%20work%2C%20we%20conduct%20a%20detailed%20study%20from%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29.%20We%20also%20revisit%20earlier%20observations%20including%20SUMER%20and%20HRTS%2C%20and%20the%20results%20from%20Dere%20et%20al.%20%281987%29%2C%20where%20they%20reported%20path%20lengths%20in%20the%20range%20of%200.1%20to%2010%20km%20using%20HRTS%20observations%2C%20assuming%20a%20similar%20formation%20temperature%20for%20C%20IV%20and%20O%20IV.%20We%20have%20used%20the%20weaker%20O%20IV%20lines%20to%20estimate%20electron%20densities%20and%20the%20path-lengths%20with%20IRIS%2C%20using%20a%20similar%20method.%20However%2C%20we%20have%20made%20certain%20improvements.%20The%20improved%20CHIANTI%20model%20now%20includes%20density%20effects%2C%20photo-ionization%2C%20and%20charge%20transfer%20%28Dufresne%20et%20al.%2C%202021a%2C%202021b%29.%0A%0AFig.%201%20shows%20a%20comparison%20of%20the%20contribution%20functions%20of%20lines%20from%20O%20IV%2C%20S%20IV%2C%20and%20Si%20IV%20at%20a%20constant%20pressure%20of%203%20%26times%3B%20%20%5Cbegin%7Bequation%7D10%5E%7B14%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%20K%20using%20CHIANTI%20and%20the%20improved%20ionization%20equilibrium%20model.%20The%20solid%20lines%20represent%20the%20contribution%20functions%20of%20different%20ions%20using%20the%20improved%20ionization%20equilibrium%20while%20the%20dashed%20lines%20represent%20CHIANTI%20values%20with%20zero-density%20effects."},{"type":"image","file":"","url":"nuggetvideos/2022/10/25/pod_polito_vanessa_2022-10-25T17%3A48%3A34.066Z/Screen Shot 2022-11-14 at 12.45.45 PM.png","hash":"c87b670e8233ad0aaa5c2268589cc079","mimeType":"image/png","caption":"Fig%201%3A%20The%20contribution%20functions%20denoted%20by%20G%28T%29%20for%20the%20O%20IV%201401.16%20%26Aring%3B%2C%20S%20IV%201406%20%26Aring%3B%2C%20and%20Si%20IV%201393.75%20%26Aring%3B%20lines.%20The%20dashed%20lines%20indicate%20CHIANTI%20while%20the%20solid%20lines%20use%20improved%20ionization%20equilibrium%20files."},{"type":"text","text":"Fig.%202%20uses%20QS%20data%20near%20the%20disc%20centre%20with%20very%20large%20dense%20raster%20observations%20taken%20on%2022nd%20October%202013%20during%2011%3A30%20-%2015%3A05%20UT.%20Fig.%203%20observes%20%20QS%20data%20near%20the%20North%20polar%20limb%20with%20a%20dense%20synoptic%20raster%20observation%20taken%20on%2022nd%20January%202014%20during%2001%3A48%20-%2002%3A15%20UT.%20%0A%0AWe%20use%20ratios%20from%20weak%20O%20IV%20lines%20%281401.7%20and%201406.5%29%20as%20density%20diagnostics.%20Assuming%20an%20isothermal%20plasma%20and%20peak%20formation%20temperature%20for%20O%20IV%20of%20Log%20T%20%3D%205.1%2C%20we%20use%20the%20densities%20calculated%20from%20O%20IV%20%20to%20derive%20the%20path%20lengths%20shown%20in%20the%20right%20bottom%20panel%20of%20Fig.%202%20and%203."},{"type":"image","file":"","url":"nuggetvideos/2022/10/25/pod_polito_vanessa_2022-10-25T17%3A48%3A34.066Z/Screen Shot 2022-11-14 at 12.49.29 PM.png","hash":"edc30ffe47ce7b8947f5aa1346dba160","mimeType":"image/png","caption":"Fig%202%3A%20The%20estimation%20of%20path%20lengths%20for%20the%20QS%20near%20the%20disc%20centre%20observed%20on%2022nd%20October%202013%20with%20an%20exposure%20time%20of%2030s.%20Top-left%20panel%20shows%20the%20ratios%20of%20the%20radiance%20of%20the%20O%20IV%201404%2F1401%20%26Aring%3B%20lines.%20Top-right%20panel%20shows%20the%20densities%20derived%20from%20the%20O%20IV%20ratio%20values.%20Bottom-left%20panel%20indicates%20the%20temperature%20calculated%20by%20the%20O%20IV%201401%2FS%20IV%201406%20%26Aring%3B%20line%20ratios.%20Bottom-right%20panel%20shows%20the%20path%20lengths%20estimated%20using%20densities%20from%20the%20O%20IV%20lines%20and%20considering%20an%20isothermal%20formation%20temperature%20of%20O%20IV%20at%20log%20T%5BK%5D%20%3D%205.1."},{"type":"image","file":"","url":"nuggetvideos/2022/10/25/pod_polito_vanessa_2022-10-25T17%3A48%3A34.066Z/Screenshot 2022-11-10 at 10.54.01 AM.png","hash":"14c6269fe31c05e9a87d3a609b984553","mimeType":"image/png","caption":"Fig.%203%3A%20The%20estimation%20of%20path%20lengths%20for%20the%20QS%20close%20to%20the%20limb%20observed%20on%2022nd%20January%202014%20with%20an%20exposure%20time%20of%2015s.%20Top-left%20panel%20shows%20the%20ratios%20of%20the%20radiance%20of%20O%20IV%201401%2F1401%20%26Aring%3B%20lines.%20Top-right%20panel%20shows%20the%20densities%20derived%20from%20O%20IV%20ratio%20values.%20Bottom-left%20panel%20indicates%20the%20temperature%20calculated%20by%20O%20IV%201401%2FS%20IV%201406%20%26Aring%3B%20line%20ratios.%20Bottom-right%20panel%20shows%20the%20path%20lengths%20estimated%20by%20using%20densities%20from%20the%20O%20IV%20lines%20and%20considering%20an%20isothermal%20formation%20temperature%20of%20O%20IV%20at%20log%20T%20%5BK%5D%20%3D%205.1."},{"type":"text","text":"We%20observe%20that%20the%20density-sensitive%20O%20IV%20lines%20provide%20typical%20averaged%20densities%20around%20%5Cbegin%7Bequation%7D10%5E%7B10%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D.These%20values%20were%20found%20to%20be%20consistent%20with%20the%20values%20reported%20in%20earlier%20publications%20using%20different%20instruments.%20We%20assessed%20the%20effects%20of%20the%20new%20atomic%20models%20on%20the%20results.%20We%20found%20centre-to-limb%20variations%20of%20path%20lengths.%20The%20median%20value%20is%20observed%20to%20be%2010%20km%20near%20the%20disc-centre%20while%20it%20increases%20to%2031%20km%20for%20the%20limb%20dataset.%20These%20values%20are%20higher%20than%20those%20reported%20in%20Dere%20et%20al.%20%281987%29.%20The%20discrepancies%20can%20be%20attributed%20to%20various%20factors%20like%20the%20assumed%20abundances.%20We%20also%20show%20that%20performing%20an%20emission%20measure%20analysis%20lowers%20significantly%20the%20path%20lengths.%20A%20centre-to-limb%20variation%20in%20the%20non-thermal%20widths%20was%20also%20observed%20with%20IRIS%20%28Rao%20et%20al.%2C%202022%29.%20Thanks%20to%20the%20high-resolution%20of%20data%20from%20IRIS%2C%20we%20were%20able%20to%20make%20direct%20calculations%20of%20path%20lengths%20in%20the%20quiet-Sun%20transition%20region%20using%20OIV.%20Such%20small%20path%20lengths%20should%20be%20taken%20into%20account%20when%20modelling%20the%20transition%20region.%20Observations%20from%20other%20instruments%20of%20small%20features%20in%20H%28alpha%29%20%2C%20Mg%20II%2C%20and%20Si%20IV%20show%20widths%20narrower%20than%202%27%27%2C%20%28De%20Pontieu%20et%20al.%2C%202021%29%2C%20indicating%20very%20small%20filling%20factors%20in%20the%20transition%20region."}],"references":["Dere K. P., Bartoe J. D. F., Brueckner G. E., Cook J. W., Socker D. G., 1987, Sol. Phys., 114, 223","Del Zanna G., Mason H. E., 2018, Living Reviews in Solar Physics, 15, 5","Dufresne R. P., Del Zanna G., Badnell N. R., 2021a, MNRAS, 503, 1976","Dufresne R. P., Del Zanna G., Storey P. J., 2021b, MNRAS, 505, 3968","De Pontieu B., et al., 2021, Sol. Phys., 296, 84","Rao et al., MNRAS, Volume 517, Issue 1, November 2022","","","",""],"pubDate":"2022-11-14T20:43:44.545Z"},{"id":"pod_polito_vanessa_2022-09-26T15:31:02.475Z","submitter":"Nancy Narang (nancy.narang@astro.uio.no)","author":"Nancy Narang [1,2], Kalugodu Chandrashekhar [1,2], Shahin Jafarzadeh [1,2], Bernhard Fleck [3], Mikolaj Szydlarski [1,2], Sven Wedemeyer [1,2]","status":"published","creation-date":"2022-09-26T15:31:02.516Z","last-modified-date":"2022-10-12T15:22:38.531Z","credit":"[1] Rosseland Centre for Solar Physics, University of Oslo, [2] Institute of Theoretical Astrophysics, University of Oslo, [3] ESA Science and Operations Department, c/o NASA Goddard Space Flight Center","title":"Power distribution of oscillations in the atmosphere of a plage region: Joint observations with ALMA, IRIS and SDO","contentBlocks":[{"type":"text","text":"The%20solar%20chromosphere%20is%20a%20vast%20reservoir%20of%20magnetohydrodynamic%20wave%20energy%2C%20with%20numerous%20complex%20structures%20showing%20a%20variety%20of%20oscillatory%20phenomena%20over%20a%20wide%20range%20of%20magnetic%20environments.%20The%20ubiquitous%20oscillations%20are%20coupled%20in%20several%20ways%20within%20the%20solar%20atmospheric%20layers%20and%20are%20one%20of%20the%20candidates%20for%20chromospheric%20and%20coronal%20heating%20%28see%20the%20review%20by%20Jess%20et%20al.%202015%29.%0A%0AIn%20the%20present%20study%20%28Narang%20et%20al.%202022%29%2C%20we%20describe%20the%20analysis%20of%20the%20distribution%20of%20oscillations%20over%20a%20range%20of%20periods%20in%20an%20active%20region%20%28NOAA%20AR12651%29%20plage%20observed%20jointly%20with%20the%20Atacama%20Large%20Millimeter%2FSubmillimeter%20Array%20%28ALMA%3B%20Wootten%20%26amp%3B%20Thompson%202009%29%2C%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%3B%20De%20Pontieu%20et%20al.%202014%29%2C%20and%20the%20Atmospheric%20Imaging%20Assembly%20%28AIA%3B%20Lemen%20et%20al.%202012%29%20on%20board%20the%20Solar%20Dynamics%20Observatory%20%28SDO%29.%20These%20coordinated%20solar%20observations%20of%20ALMA%20with%20IRIS%20and%20SDO%20provide%20a%20unique%20opportunity%20to%20study%20the%20solar%20atmosphere%20at%20millimeter%20wavelengths%20in%20conjunction%20with%20the%20ultraviolet%20part%20of%20the%20solar%20spectrum%20%28see%20the%20review%20on%20potentials%20of%20ALMA%20observations%20by%20Wedemeyer%20et%20al.%202016%29.%0A%0AIn%20this%20study%20we%20explore%20the%20presence%20of%20possible%20associations%20of%20ALMA%20observations%20with%20chromospheric%20and%20lower%20coronal%20observations%20from%20IRIS%20and%20AIA%20from%20the%20point%20of%20view%20of%20oscillations.%20The%20plage%20region%20studied%20is%20shown%20in%20the%20top%20panels%20of%20Figure%201%20within%20a%20larger%20FOV%20of%20a%20representative%20HMI%20LOS%20magnetogram%20and%20IRIS%202796%20%26Aring%3B%20slit-jaw%20image%20%28SJI%29.%20The%20first%20frames%20of%20the%20studied%20FOV%20of%20the%20different%20passbands%20are%20shown%20in%20the%20bottom%20panels.%20This%20coordinated%20data%20set%20is%20one%20of%20the%20first%20campaigns%20where%20joint%20observations%20between%20ALMA%20and%20IRIS%20were%20conducted%20and%20good%20alignment%20between%20ALMA%20and%20IRIS%20data%20sets%20was%20achieved%20%28see%20details%20in%20Henriques%20et%20al.%202021%29."},{"type":"image","file":"","url":"nuggetvideos/2022/09/26/pod_polito_vanessa_2022-09-26T15%3A31%3A02.475Z/fig1_irisnug.png","hash":"b57c6fcd94168ab53137c1c1dd858a3c","mimeType":"image/png","caption":"Figure%201%3A%20Context%20images%20showing%20the%20HMI%20LOS%20magnetogram%20in%20panel%20%28a%29%20and%20the%20IRIS%202796%20%26Aring%3B%20SJI%20in%20panel%20%28b%29%20at%20the%20start%20time%20of%20the%20ALMA%20observations.%20The%20FOV%20studied%20is%20marked%20by%20the%20green%20circle%20in%20panels%20%28a%29%20and%20%28b%29.%20Panels%20%28c%29%20to%20%28j%29%20show%20the%20representative%20images%20of%20the%20studied%20FOV%20%28from%20ALMA%20Band%206%2C%20IRIS%20SJI%202796%20%26Aring%3B%2C%20and%20different%20AIA%20channels%2C%20as%20indicated%20on%20top%20of%20the%20panels%29%20at%20the%20start%20time%20of%20the%20observations."},{"type":"text","text":"We%20study%20the%20spatial%20association%20of%20oscillations%20through%20the%20atmosphere%2C%20with%20a%20focus%20on%20the%20correlation%20of%20the%20power%20distribution%20of%20ALMA%20oscillations%20with%20other%20passbands.%20We%20perform%20Lomb-Scargle%20%28LS%29%20transforms%20to%20study%20the%20distribution%20of%20oscillation%20power%20by%20means%20of%20dominant%20period%20maps%20%28Figure%202%29.%20The%20distribution%20of%20the%20dominant%20periods%2C%20shown%20in%20Figure%202%20%26amp%3B%203%2C%20reveals%20the%20presence%20of%20oscillations%20over%20a%20wide%20range%20of%20periods%20%28up%20to%2035%20min%29%20in%20this%20plage%20region%2C%20with%2012%E2%80%9314min%20prominent%20in%20the%20ALMA%20and%20AIA%20coronal%20passbands.%20On%20the%20other%20hand%2C%20the%20chromospheric%20and%20transition%20region%20passbands%20of%20IRIS%20and%20AIA%20show%20a%20prominence%20of%20shorter%20periods%20of%20about%203%E2%80%936%20min."},{"type":"image","file":"","url":"nuggetvideos/2022/09/26/pod_polito_vanessa_2022-09-26T15%3A31%3A02.475Z/figure2.png","hash":"f3c5d0176b98c01b2545d2655e913dfa","mimeType":"image/png","caption":"Figure%202%3A%20Dominant%20Period%20maps%20produced%20by%20performing%20LS%20transforms%20over%20the%20full%20FOV%20of%20the%20eight%20passbands%20studied%20here."},{"type":"image","file":"","url":"nuggetvideos/2022/09/26/pod_polito_vanessa_2022-09-26T15%3A31%3A02.475Z/figure3.png","hash":"7a9489eca089fe6a02f54aa257ec72b","mimeType":"image/png","caption":"Figure%203%3A%20Histograms%20of%20dominant%20periods%20%28grey%29%20detected%20over%20the%20FOV%20in%20the%20eight%20passbands.%20Overplotted%20in%20blue%20are%20the%20average%20power%20spectra%20for%20the%20respective%20passband."},{"type":"text","text":"The%20oscillations%20with%203%E2%80%935%20min%20periods%20in%20the%20chromosphere%20are%20well%20understood%20and%20are%20explained%20as%20the%20basic%20cutoff%20frequency%20resonance%20of%20the%20chromosphere%20%28Rutten%201995%29.%20Recent%20numerical%20models%20and%20simulations%20have%20predicted%20ALMA%20to%20probe%20plasma%20conditions%20in%20the%20mid-to-high%20chromosphere%20%28Mart%26iacute%3Bnez-Sykora%20et%20al.%202020%29.%20The%20very%20different%20global%20behavior%20of%20ALMA%20oscillations%20in%20comparison%20to%20other%20chromospheric%20passbands%20studied%20here%20indicates%20the%20need%20for%20more%20detailed%20investigations%20to%20determine%20the%20formation%20height%20of%20the%20radiation%20observed%20by%20ALMA%20%28also%20see%20Jafarzadeh%20et%20al.%202021%29.%0A%0AWhile%20the%20global%20behavior%20of%20the%20dominant%20ALMA%20oscillations%20shows%20some%20similarity%20with%20that%20of%20the%20transition%20region%20and%20coronal%20passbands%20of%20AIA%2C%20the%20ALMA%20dominant%20period%20map%20do%20not%20show%20significant%20association%20with%20those%20from%20the%20other%20passbands.%20As%20shown%20in%20the%20scatter%20plots%20in%20Figure%204%2C%20the%20ALMA%20dominant%20period%20map%20do%20not%20show%20any%20spatial%20correlation%20with%20the%20respective%20ones%20from%20the%20other%20passbands%2C%20with%20all%20the%20cross-correlation%20coefficients%20less%20than%203%25."},{"type":"image","file":"","url":"nuggetvideos/2022/09/26/pod_polito_vanessa_2022-09-26T15%3A31%3A02.475Z/figure4.png","hash":"129c51b4512405713d8434fdfbce5fb1","mimeType":"image/png","caption":"Figure%204%3A%20Scatter%20plot%20between%20the%20ALMA%20Band-6%20dominant%20period%20map%20and%20that%20from%20IRIS%202796%20%26Aring%3B%20in%20panel%20%28a%29%3B%20and%20different%20AIA%20channels%20in%20panels%20%28b%29%20to%20%28g%29.%20The%20value%20of%20the%20cross-correlation%20coefficient%20%28cc%29%20is%20shown%20to%20the%20top%20right%20of%20each%20panel."},{"type":"text","text":"We%20speculate%20that%20the%20non-association%20of%20ALMA%20oscillations%20with%20those%20of%20IRIS%20and%20AIA%20is%20due%20to%20significant%20variations%20in%20the%20height%20of%20formation%20of%20the%20millimeter%20continuum%20observed%20by%20ALMA.%20A%20better%20understanding%20of%20the%20range%20of%20the%20formation%20height%20of%20the%20radiation%20observed%20by%20ALMA%20will%20help%20to%20explain%20the%20specific%20reasons%20for%20such%20non-associated%20behavior%20of%20ALMA%20oscillations%20with%20the%20IRIS%20and%20AIA%20oscillations.%0A%0AAdditionally%2C%20the%20fact%20that%20ALMA%20directly%20maps%20the%20brightness%20temperature%2C%20in%20contrast%20to%20the%20intensity%20observations%20by%20IRIS%20and%20AIA%2C%20can%20result%20in%20the%20very%20different%20intrinsic%20nature%20of%20the%20ALMA%20oscillations%20compared%20to%20the%20IRIS%20and%20AIA%20oscillations.%20The%20complex%20interrelation%20between%20the%20nature%20of%20ALMA%20temperature%20oscillations%20with%20the%20IRIS%2FAIA%20intensity%20oscillations%20need%20to%20be%20explored%20in%20detail.%0A%0AFurther%20statistical%20investigations%20using%20multiple%20coordinated%20observations%20spanning%20a%20variety%20of%20solar%20features%20in%20quiet%20Sun%2C%20coronal%20hole%2C%20and%20active%20regions%2C%20complemented%20with%20numerical%20models%2C%20should%20help%20to%20better%20understand%20the%20nature%20of%20the%20oscillations%20observed%20with%20ALMA%2C%20and%20thus%20its%20association%20with%20other%20observations."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2015SSRv..190..103J\">Jess, D. B., Morton, R. J., Verth, G., et al. 2015, Space Sci. Rev., 190, 103</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022A&A...661A..95N\">Narang, N., Chandrashekhar, K., Jafarzadeh, S., et al. 2022, A&A, 661, A95</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2009IEEEP..97.1463W\">Wootten, A. & Thompson, A. R. 2009, IEEE Proceedings, 97, 1463</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D\">De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Sol. Phys., 289, 2733</a>","<a href=\"http://adsabs.harvard.edu/abs/2012SoPh..275...17L\">Lemen, J. R., Title, A. M., Akin, D. J., et al. 2012, Sol. Phys., 275, 17</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016SSRv..200....1W\">Wedemeyer, S., Bastian, T., Brajsa, R., et al. 2016, Space Sci. Rev., 200, 1</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022A&A...659A..31H\">Henriques, V. M. J., Jafarzadeh, S., Guevara Gomez, J. C., et al. 2022, A&A, 659, A31</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1995ESASP.376a.151R\">Rutten, R. J. 1995, in ESA Special Publication, Vol. 376, Helioseismology, ed. J. T. Hoeksema, V. Domingo, B. Fleck, & B. Battrick, 151</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...891L...8M\">Martinez-Sykora, J., De Pontieu, B., de la Cruz Rodriguez, J., & Chintzoglou, G.2020, ApJ, 891, L8</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021RSPTA.37900174J\">Jafarzadeh, S., Wedemeyer, S., Fleck, B., et al. 2021, Philosophical Transactionsof the Royal Society of London Series A, 379, 20200174</a>"],"pubDate":"2022-10-14T15:00:53.446Z"},{"id":"pod_polito_vanessa_2022-08-31T17:12:17.504Z","submitter":"Michael Hahn","author":"Michael Hahn[1], Xiangrong Fu[2], and Daniel Wolf Savin[1]","status":"published","creation-date":"2022-08-31T17:12:17.508Z","last-modified-date":"2022-09-13T00:39:39.845Z","credit":"[1] Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA [2] New Mexico Consortium, 4200 W. Jemez Rd. Suite 200, Los Alamos, NM 87544, USA","title":"Evidence for Parametric Decay Instability in the Lower Solar Atmosphere","contentBlocks":[{"type":"text","text":"Wave-driven%20theories%20posit%20that%20Alfv%26eacute%3Bn%20waves%20carry%20energy%20from%20lower%20layers%20of%20the%20solar%20atmosphere%20into%20the%20corona.%20These%20waves%20have%20long%20wavelengths%20and%20cannot%20directly%20heat%20the%20coronal%20plasma.%20Most%20theories%20invoke%20Alfv%26eacute%3Bnic%20turbulence%20as%20the%20mechanism%20that%20cascades%20the%20wave%20energy%20to%20the%20short%20length%20scales%20where%20wave-particle%20interactions%20cause%20plasma%20heating%20%28e.g.%2C%20Matthaeus%20et%20al.%201999%2C%20Cranmer%20et%20al.%202007%29.%20Alfv%26eacute%3Bnic%20turbulence%20is%20produced%20by%20a%20nonlinear%20interaction%20between%20counter-propagating%20Alfv%26eacute%3Bn%20waves%20%28Howes%20%26amp%3B%20Nielson%202013%29.%20This%20leads%20to%20the%20question%20as%20to%20the%20origin%20of%20the%20sunward-propagating%20Alfv%26eacute%3Bn%20waves.%20%0A%0AThe%20parametric%20decay%20instability%20%28PDI%29%20is%20one%20possible%20mechanism%20that%20can%20excite%20the%20sunward-propagating%20waves.%20In%20PDI%2C%20a%20large%20amplitude%20forward-propagating%20%E2%80%9Cpump%E2%80%9D%20Alfv%26eacute%3Bn%20wave%20can%20decay%20into%20a%20backward%20propagating%20Alfv%26eacute%3Bn%20wave%20and%20a%20forward%20propagating%20ion%20acoustic%20wave%20%28Derby%201978%29.%20Some%20numerical%20models%20have%20shown%20that%20PDI%20can%20self-consistently%20generate%20turbulence%20and%20coronal%20heating%20%28e.g.%2C%20R%26eacute%3Bville%20et%20al.%202018%2C%20Shoda%20et%20al.%202019%29.%20%0A%0AUsing%20IRIS%20data%2C%20we%20have%20found%20evidence%20for%20PDI%20in%20the%20lower%20solar%20atmosphere%20%28Hahn%20et%20al.%202022%29.%20These%20data%20come%20from%20an%20off-limb%20sit-and-stare%20observation%20of%20a%20coronal%20hole%20starting%20on%202016%20October%2031%2019%3A45%20UT%2C%20where%20the%20IRIS%20slit%20was%20oriented%20radially%20over%20the%20limb%20%28Figure%201%29.%20From%20these%20spectra%2C%20we%20extracted%20the%20intensities%20and%20Doppler%20shifts%20of%20the%20Si%20IV%20lines.%20Fluctuations%20in%20these%20quantities%20over%20time%20represent%20fluctuations%20in%20density%20and%20velocity%2C%20respectively."},{"type":"image","file":"","url":"nuggetvideos/2022/08/31/pod_polito_vanessa_2022-08-31T17%3A12%3A17.504Z/Fig1.png","hash":"f1ecb4d4405a2a54a7bb5e23ec4889b2","mimeType":"image/png","caption":"Figure%201.%20IRIS%20slit-jaw%20image%20for%20the%20observed%20region.%20The%20position%20of%20the%20spectrometer%20slit%20is%20highlighted%20by%20the%20vertical%20line."},{"type":"text","text":"The%20velocity%20fluctuations%20are%20likely%20due%20to%20Alfv%26eacute%3Bn%20waves%20and%20the%20density%20fluctuations%20from%20acoustic%20waves.%20This%20interpretation%20is%20supported%20by%20the%20inferred%20wave%20speed%20of%20about%20250%20km%2Fs%20for%20the%20velocity%20fluctuations%2C%20which%20agrees%20with%20the%20estimated%20Alfv%26eacute%3Bn%20speed%20in%20this%20region%2C%20and%20about%2075%20km%2Fs%20for%20the%20density%20fluctuations%2C%20which%20is%20roughly%20what%20is%20expected%20for%20the%20sound%20speed.%20These%20speeds%20imply%20that%20the%20plasma%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D%20%7E%200.1%2C%20where%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D%20is%20the%20ratio%20of%20the%20fluid-to-magnetic%20pressure%20and%20is%20equal%20to%20the%20square%20of%20ratio%20of%20the%20sound%20and%20Alfv%26eacute%3Bn%20speeds.%20%0A%0AWe%20performed%20a%20Fourier%20analysis%20of%20the%20density%20and%20velocity%20fluctuations%20and%20found%20that%20their%20power%20spectra%20resembled%20one%20another%2C%20except%20that%20the%20acoustic%20power%20spectrum%20is%20at%20about%20half%20the%20frequency%20of%20the%20Alfv%26eacute%3Bn%20power%20spectrum%20%28Figures%202%20and%203%29.%20This%20frequency%20scaling%20is%20consistent%20with%20the%20predictions%20for%20PDI."},{"type":"image","file":"","url":"nuggetvideos/2022/08/31/pod_polito_vanessa_2022-08-31T17%3A12%3A17.504Z/Fig2.png","hash":"ae40706cbf4e87eb97e3f1d3a3ed2051","mimeType":"image/png","caption":"Figure%202.%20Average%20power%20spectra%20for%20the%20density%20fluctuations%20%28labeled%20%CE%B4n%29%20and%20the%20velocity%20fluctuations%20%28labeled%20%5Cbegin%7Bequation%7D%5Cdelta%20v%5Cend%7Bequation%7D%29.%20The%20solid%20curve%20shows%20the%20average%20power%20spectrum%20for%20the%20density%20fluctuations%20when%20its%20frequency%20axis%20is%20multiplied%20by%20a%20factor%20of%202.%20In%20that%20case%2C%20the%20%5Cbegin%7Bequation%7D%5Cdelta%20n%5Cend%7Bequation%7D%20and%20%5Cbegin%7Bequation%7D%5Cdelta%20v%5Cend%7Bequation%7D%20power%20spectra%20are%20nearly%20aligned."},{"type":"image","file":"","url":"nuggetvideos/2022/08/31/pod_polito_vanessa_2022-08-31T17%3A12%3A17.504Z/Fig3.png","hash":"f36d89d52c06b87be8c8299ab85fc253","mimeType":"image/png","caption":"Figure%203.%20Correlation%20coefficient%20vs.%20scaling%20factor%20for%20the%20frequency%20axis%20for%20the%20%5Cbegin%7Bequation%7D%5Cdelta%20n%5Cend%7Bequation%7D%20frequency%20axis.%20The%20correlation%20coefficient%20is%20maximized%20when%20the%20scaling%20factor%20is%20about%202%2C%20implying%20that%20the%20%CE%B4n%20fluctuations%20occur%20at%20half%20the%20frequency%20of%20the%20%5Cbegin%7Bequation%7D%5Cdelta%20v%5Cend%7Bequation%7D%20fluctuations."},{"type":"text","text":"The%20maximum%20growth%20rate%20for%20PDI%20occurs%20at%20a%20frequency%20%5Cbegin%7Bequation%7D%5Comega_%7Bmax%7D%5Cend%7Bequation%7D%2C%20which%20depends%20on%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D%20and%20the%20pump%20wave%20frequency%20%5Cbegin%7Bequation%7D%5Comega_0%5Cend%7Bequation%7D.%20Figure%204%20shows%20the%20ratio%20%5Cbegin%7Bequation%7D%5Comega_%7Bmax%7D%2F%5Comega_0%5Cend%7Bequation%7D%20versus%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D.%20If%20the%20acoustic%20waves%20are%20produced%20by%20PDI%2C%20then%20they%20are%20expected%20to%20be%20found%20primarily%20at%20the%20frequency%20at%20which%20the%20PDI%20growth%20rate%20is%20a%20maximum.%20For%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D%7E%200.1%2C%20the%20predicted%20%5Cbegin%7Bequation%7D%5Comega_%7Bmax%7D%2F%5Comega_0%5Cend%7Bequation%7D%20%7E%200.5.%20This%20agrees%20with%20our%20observation%20that%20the%20acoustic%20waves%20were%20at%20half%20the%20frequency%20of%20the%20Alfv%26eacute%3Bn%20waves.%20%0A%0AFuture%20observational%20work%20will%20aim%20to%20confirm%20this%20result%20by%20looking%20for%20the%20sunward-propagating%20secondary%20Alfv%26eacute%3Bn%20waves.%20These%20were%20difficult%20to%20distinguish%20in%20this%20observation%20due%20to%20the%20relatively%20short%20height%20range%20through%20the%20transition%20region%20where%20Si%20IV%20could%20be%20observed.%20Developments%20in%20theory%20are%20also%20needed%20to%20understand%20how%20PDI%20proceeds%20in%20inhomogeneous%20plasmas.%20Studies%20relevant%20to%20the%20solar%20wind%20have%20suggested%20that%20inhomogeneity%20changes%20the%20resonance%20condition%20and%20slows%20the%20growth%20rate%20for%20PDI%20%28e.g.%2C%20Tenerani%20%26amp%3B%20Velli%202013%3B%20Shoda%20et%20al.%202018%29.%20The%20transition%20region%20we%20observed%20should%20include%20strong%20gradients%20in%20temperature%2C%20density%2C%20and%20magnetic%20field%2C%20yet%20PDI%20still%20seemed%20to%20be%20present."},{"type":"image","file":"","url":"nuggetvideos/2022/08/31/pod_polito_vanessa_2022-08-31T17%3A12%3A17.504Z/Fig4.png","hash":"287fc64f3bfd72c16341f74aa549f0ee","mimeType":"image/png","caption":"Figure%204.%20Frequency%20of%20the%20maximum%20growth%20rate%20acoustic%20mode%20relative%20to%20the%20pump%20wave%20frequency%2C%20%5Cbegin%7Bequation%7D%5Cdelta%20B%2FB_0%5Cend%7Bequation%7D%20%2C%20versus%20%5Cbegin%7Bequation%7D%5Cbeta%5Cend%7Bequation%7D%20for%20PDI.%20%5Cbegin%7Bequation%7D%5Comega_%7Bmax%7D%2F%5Comega_0%5Cend%7Bequation%7D%20is%20the%20pump%20Alfven%20wave%20amplitude%20normalized%20by%20the%20mean%20magnetic%20field.%20The%20curves%20four%20values%20of%20%5Cbegin%7Bequation%7D%5Cdelta%20B%2FB_0%5Cend%7Bequation%7D%20overlap%20in%20the%20figure.%20See%20Hahn%20et%20al.%20%282022%29."},{"type":"text","text":"Finally%2C%20we%20note%20that%20this%20observation%20looked%20at%20a%20generic%20coronal%20hole%20region.%20If%20PDI%20is%20present%20there%2C%20then%20it%20is%20likely%20to%20be%20present%20in%20many%20regions%20of%20the%20corona.%20PDI%20may%20be%20a%20common%20process%20that%20mediates%20the%20transfer%20of%20energy%20from%20Alfv%26eacute%3Bn%20waves%20into%20coronal%20heating."}],"references":["<a href=\" https://ui.adsabs.harvard.edu/abs/2007ApJS..171..520C/abstract\">Cranmer, S. R., van Ballegooijen, A. A., & Edgar, R. J. 2007, ApJS, 171, 520 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1978ApJ...224.1013D/abstract\">Derby, N. F., Jr. 1978, ApJ, 224, 1013 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...933...52H/abstract\">Hahn, M., Fu, F., & Savin, D. W. 2022, ApJ, 933, 52 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2013PhPl...20g2302H/abstract\">Howes, G. G., & Nielson, K. D. 2013, PhPl, 20, 072302 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1999ApJ...523L..93M/abstract\">Matthaeus, W. H., Zank, G. P., Oughton, S., Mullan, D. J., & Dmitruk, P. 1999, ApJL, 523, L93 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...866...38R/abstract\">Réville, V., Tenerani, A., & Velli, M. 2018, ApJ, 866, 38 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...860...17S/abstract\">Shoda, M., Yokoyama, T., & Suzuki, T. K. 2018, ApJ, 860, 17 </a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2019ApJ...880L...2S/abstractâÂÂÂÂÂÂÂÂÂÂÂÂ\">Shoda, M., Suzuki, T. K., Asgari-Targhi, M., & Yokoyama, T. 2019, ApJL, 880, L2 </a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2013JGRA..118.7507T/abstractâÂÂÂÂÂÂÂÂÂÂÂÂ\">Tenerani, A., & Velli, M. 2013, JGR, 118, 7507 </a>",""],"pubDate":"2022-09-13T00:34:05.474Z"},{"id":"pod_polito_vanessa_2022-07-26T17:18:13.573Z","submitter":"Juraj Lorincik","author":"Juraj Lorincik[1, 2], Jaroslav Dudik[3], Vanessa Polito[1, 2]","status":"published","creation-date":"2022-07-26T17:18:13.577Z","last-modified-date":"2022-08-09T08:21:42.363Z","credit":"[1] - Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA [2] - Lockheed Martin Solar & Astrophysics Laboratory, Org. A021S, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304, USA [3] - Astronomical Institute of the Czech Academy of Sciences, Fricova 298, 251 65 Ondrejov, Czech Republic","title":"Blueshifted Si IV 1402.77A line profiles in a moving flare kernel observed by IRIS","contentBlocks":[{"type":"text","text":"Spectroscopic%20observations%20of%20solar%20flare%20ribbons%20provide%20a%20wealth%20of%20information%20about%20the%20deposition%20of%20energy%20released%20during%20solar%20flares.%20Spectra%20of%20lines%20formed%20at%20coronal%20and%20flare%20temperatures%20of%20the%20order%20of%201%E2%80%9410%20MK%20often%20show%20signatures%20of%20upflows%20existing%20as%20a%20consequence%20of%20the%20chromospheric%20evaporation.%20Cooler%20lines%20of%20the%20chromosphere%20and%20the%20transition%20region%20are%20often%20redshifted%20due%20to%20the%20downflow-inducing%20chromospheric%20condensation.%20Very%20rarely%2C%20these%20lines%20can%20also%20exhibit%20blueshifts%2C%20which%20have%20been%20detected%20in%20small%20flares%20%28e.g.%2C%20Li%20et%20al.%202019%29%20and%20micro-%20and%20nano-sized%20flare%20events%20%28Testa%20et%20al.%202014%2C%20Polito%20et%20al.%202018%29.%20Interface%20Region%20Imaging%20Spectrometer%20%28IRIS%3B%20De%20Pontieu%20et%20al.%202014%29%20provides%20flare%20observations%20at%20high%20spatial%20and%20temporal%20resolutions%20which%20makes%20it%20an%20ideal%20instrument%20to%20study%20individual%20flare%20kernels%2C%20the%20building%20bricks%20of%20ribbons%20%28e.g.%20Graham%20%26amp%3B%20Cauzzi%202015%29.%20During%20impulsive%20phases%20of%20flares%2C%20kernels%20exhibit%20motions%20primarily%20oriented%20along%20the%20ribbons%20%28e.g.%2C%20L%26ouml%3Brin%C4%8D%26iacute%3Bk%20et%20al.%202019%29%20as%20a%20consequence%20of%20the%20magnetic%20slipping%20reconnection%20%28see%20Dud%26iacute%3Bk%20et%20al.%202014%20and%20the%20review%20of%20Janvier%202017%29.%20Several%20spectroscopic%20studies%20showed%20that%20various%20properties%20of%20ribbon%20spectra%20can%20be%20attributed%20to%20the%20slipping%20reconnection%20%28e.g.%20Li%20%26amp%3B%20Zhang%202015%29.%20%0A%0AIn%20L%26ouml%3Brin%C4%8D%26iacute%3Bk%20et%20al.%20%282022%29%20we%20investigate%20the%20spatial%20and%20temporal%20evolution%20of%20transient%20blueshifts%20exhibited%20by%20spectra%20observed%20in%20a%20moving%20%28slipping%29%20flare%20kernel.%20We%20used%20IRIS%20observations%20of%20the%202015%20June%2022%20M6.5-class%20flare%20acquired%20in%20the%20sparse%20raster%20mode%20at%20a%20very%20high%20cadence%20of%201%20s.%20This%20let%20us%20study%20both%20spatial%20and%20temporal%20variations%20in%20profiles%20of%20transition%20region%20and%20chromospheric%20lines%2C%20mainly%20the%20Si%20IV%201402.77%20%26Aring%3B%20line%2C%20in%20a%20selected%20kernel%20during%20its%20motion%20along%20a%20ribbon%20that%20formed%20during%20the%20flare%20%28Figure%201a%29%29.%20The%20commencing%20and%20final%20locations%20of%20the%20motion%20of%20the%20analyzed%20kernel%20are%20plotted%20in%20panels%20Figure%201b%29%20and%20c%29.%20SDO%2FAIA%20131%26Aring%3B%20observations%20of%20apparently-slipping%20flare%20loops%2C%20one%20of%20which%20%28pink%20arrow%29%20was%20rooted%20in%20this%20kernel%2C%20are%20shown%20in%20Figure%201d%29."},{"type":"image","file":"","url":"nuggetvideos/2022/07/26/pod_polito_vanessa_2022-07-26T17%3A18%3A13.573Z/Figure1.png","hash":"220269d19113ac43f7be860d88137b6e","mimeType":"image/png","caption":"Figure%201%3A%20Context%201400%20SJI%20observations%20of%20flare%20ribbons%20%28panel%20a%29%29%20and%20kernel%20moving%20along%20the%20north-eastern%20ribbon%20%28panels%20b%29%E2%80%94c%29%29.%20Panel%20d%29%20shows%20apparently-slipping%20flare%20loops%20in%20the%20AIA%20131%20%26Aring%3B%20channel.%20The%20white%20arrow%20in%20panel%20b%29%20indicates%20the%20direction%20of%20the%20solar%20north.%20The%20pink%20arrow%20marks%20the%20flare%20loop%20footpoint%20corresponding%20to%20the%20bright%20kernel%20visible%20in%20panel%20c%29."},{"type":"image","file":"","url":"nuggetvideos/2022/07/26/pod_polito_vanessa_2022-07-26T17%3A18%3A13.573Z/Figure2.png","hash":"1e28da375c045b64a4b1e7b49677f9aa","mimeType":"image/png","caption":"Figure%202%3A%20Integrated%20intensity%20%28panels%20a%29%E2%80%94c%29%29%20and%20the%20Doppler%20shift%20of%20the%20centroid%20of%20the%20Si%20IV%201402.77%20%26Aring%3B%20line%20in%20the%20analyzed%20kernel.%20The%20inclusions%20plotted%20in%20panels%20h%29%20and%20i%29%20provide%20a%20zoomed%20view%20of%20a%20small%20region%20where%20the%20line%20exhibited%20blueshifts."},{"type":"text","text":"We%20inspected%20the%20characteristics%20of%20the%20Si%20IV%201402.77%20%26Aring%3B%20line%20in%20maps%20of%20the%20line%20intensity%20%28Figure%202a%29%E2%80%94e%29%29%20and%20the%20Doppler%20velocity%20%28Figure%202f%29%E2%80%94j%29%29%20corresponding%20to%20the%20line%20centroid%20obtained%20via%20moment%20analysis.%20As%20indicated%20by%20the%20second%20row%20of%20this%20figure%2C%20the%20peaks%20of%20this%20line%20were%20redshifted%20in%20most%20locations%2C%20which%20is%20typical%20in%20flare%20ribbons.%20An%20exception%20is%20however%20seen%20in%20panel%20h%29%20which%20shows%20that%20the%20line%20also%20exhibited%20short-lived%20blueshifts%20of%20up%20to%20%5Cbegin%7Bequation%7D%7Cv_%5Cmathrm%7BD%7D%7C%20%3D%2055%5Cend%7Bequation%7D%20km%20%5Cbegin%7Bequation%7D%5Cmathrm%7Bs%7D%5E%7B-1%7D%5Cend%7Bequation%7D%20concentrated%20in%20a%20small%20region%20corresponding%20to%20the%20moving%20kernel.%20This%20behavior%20was%20also%20exhibited%20by%20the%20chromospheric%20lines%20of%20C%20II%201334%20%26amp%3B%201335%20%26Aring%3B%20as%20well%20as%20Mg%20II%20k%20%282796%20%26Aring%3B%29.%20The%20time%20evolution%20of%20their%20profiles%20in%20the%20pixels%20marked%20using%20the%20circle%20and%20diamond%20symbols%20in%20Figure%202h%29%20is%20shown%20in%20Figure%203.%20When%20the%20kernel%20entered%20the%20selected%20pixel%20locations%20%28blue%20profiles%29%2C%20the%20line%20profiles%20exhibited%20weak%20blueshifts%20and%20blue%20wing%20enhancements.%20In%20the%20consecutive%20raster%20%28red%20profiles%29%2C%20the%20lines%20again%20exhibited%20redshifts%20and%2For%20pronounced%20red%20wings."},{"type":"image","file":"","url":"nuggetvideos/2022/07/26/pod_polito_vanessa_2022-07-26T17%3A18%3A13.573Z/Figure3.png","hash":"d7a98bbe93ac9387abc94a2d19174170","mimeType":"image/png","caption":"Figure%203%3A%20Temporal%20evolution%20of%20the%20C%20II%201334.53%2C%201355.66%2C%20and%201335.71%20%26Aring%3B%20as%20well%20as%20the%20Mg%20II%20k%20%282796.35%20%26Aring%3B%29%20line%20in%20two%20pixels%20marked%20using%20the%20circle%20and%20diamond%20symbols%20in%20Figure%202h%29.%20The%20spectra%20were%20binned%20to%20increase%20the%20signal-to-noise%20ratio%20and%20were%20normalized%20to%20unity."},{"type":"text","text":"The%20fact%20that%20the%20blueshifts%20were%20localized%20in%20both%20time%20and%20space%20motivated%20us%20to%20investigate%20the%20kernel%E2%80%99s%20motion%20at%20a%20greater%20detail.%20We%20used%20AIA%20304%20%26Aring%3B%20observations%20to%20track%20the%20moving%20kernel%20in%20regions%20with%20varying%20strength%20of%20the%20photospheric%20magnetic%20field%20measured%20by%20HMI%20onboard%20SDO%20%28Figure%204a%29%29.%20The%20positions%20of%20the%20kernel%20in%20time%20%28colored%20asterisks%20in%20Figure%204b%29%29%20indicate%20that%20after%20moving%20along%20the%20edge%20of%20a%20strong-field%20region%20%28red%20and%20yellow%20asterisks%29%2C%20the%20kernel%20entered%20a%20weak-field%20region%20%28green%20and%20blue%20asterisks%29%20from%20which%20it%20accelerated%20and%20moved%20toward%20the%20north%20direction%20%28violet%20and%20black%20asterisk%29.%20The%20blue%20frame%20plotted%20in%20the%20same%20panel%2C%20marking%20the%20location%20where%20IRIS%20observed%20the%20Si%20IV%20blueshifts%2C%20is%20co-spatial%20with%20the%20weak-field%20region%20in%20which%20the%20kernel%20accelerated.%20This%20suggests%20that%20the%20transient%20blueshifts%20were%20likely%20driven%20by%20the%20change%20in%20kernel%20dynamics%20dictated%20by%20the%20magnetic%20field%2C%20as%20reported%20by%20L%26ouml%3Brin%C4%8D%26iacute%3Bk%20et%20al.%20%282019%29%20in%20their%20analysis%20of%20a%20different%20event."},{"type":"image","file":"","url":"nuggetvideos/2022/07/26/pod_polito_vanessa_2022-07-26T17%3A18%3A13.573Z/Figure4.png","hash":"15a44f9aa7f143051005a83d36bbc2fe","mimeType":"image/png","caption":"Figure%204%3A%20Maps%20of%20HMI%20%5Cbegin%7Bequation%7D%20B_%7B%5Cmathrm%7BLOS%7D%7D%5Cend%7Bequation%7D%20in%20the%20region%20where%20the%20motion%20of%20the%20kernel%20was%20observed%20saturated%20to%20%2B%2F-%201500%20G%20%28panel%20a%29%29%20and%20%2B%2F-%20400%20G%20%28panel%20b%29%29.%20The%20red%20contours%20plotted%20in%20panel%20b%29%20correspond%20to%20%5Cbegin%7Bequation%7D%20B_%7B%5Cmathrm%7BLOS%7D%7D%5Cend%7Bequation%7D%20%3D%200%20G%20and%20indicate%20the%20polarity%20inversion%20lines.%20The%20black%20arrow%20plotted%20in%20the%20same%20panel%20indicates%20the%20direction%20of%20the%20motion%20of%20the%20kernel%20before%20the%20period%20of%20interest.%20Positions%20of%20the%20kernel%20as%20observed%20in%20the%20AIA%20304%20%26Aring%3B%20channel%20are%20marked%20using%20the%20colored%20asterisks.%20The%20blue%20frame%20marks%20the%20region%20where%20the%20Si%20IV%20blueshifts%20were%20observed."},{"type":"text","text":"In%20summary%2C%20the%20high%20spatial%20and%20temporal%20resolution%20of%20IRIS%20let%20us%20study%20varying%20properties%20of%20transition%20region%20and%20chromospheric%20lines%20in%20a%20moving%20kernel.%20We%20particularly%20focused%20on%20short-living%20blueshifts%20concentrated%20in%20one%20small%20region%20exhibited%20by%20the%20Si%20IV%201402.77%20%26Aring%3B%20line.%20By%20combining%20the%20spectroscopic%20and%20imaging%20observations%20with%20the%20measurements%20of%20the%20magnetic%20field%20we%20found%20that%20the%20blueshifts%20occurred%20during%20the%20acceleration%20of%20the%20kernel%20upon%20entering%20a%20weak-field%20region.%20This%20indicates%20that%20spatial%20variations%20in%20the%20distribution%20of%20the%20local%20magnetic%20field%20affect%20both%20the%20properties%20of%20the%20apparent%20slipping%20motion%20and%20the%20characteristics%20of%20spectra%20observed%20in%20ribbons.%20%0A%0AFor%20further%20details%20see%20L%26ouml%3Brin%C4%8D%26iacute%3Bk%20et%20al.%20%282022%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu, B., Title, A. M., Lemen, J. R., et al., SoPh, 289, 2733 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014ApJ...784..144D/abstract\">Dudik, J., Janvier, M., Aulanier, G., et al., ApJ, 784, 144 (2014)</a>","<a href=\" https://ui.adsabs.harvard.edu/abs/2015ApJ...807L..22G /abstract\"> Graham, D. R., & Cauzzi, G., ApJL, 807, L22 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017JPlPh..83a5301J/abstract\">Janvier, M., JPP, 83, 535830101 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...804L...8L/abstract\">Li, T., & Zhang, J., ApJL, 804, L8 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...879...30L/abstract\">Li, Y., Ding, M. D., Hong, J., Li, H., & Gan, W. Q., ApJ, 879, 30 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...881...68L/abstract\">Lorincik, J., Aulanier, G., Dudik, J., Zemanova, A., Dzifacova, E., ApJ, 881, 68 (2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022arXiv220610114L/abstract\">Lorincik, J., Dudik, J., Polito, V., eprint arXiv:2206.10114 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...856..178P/abstract\">Polito, V., Testa, P., Allred, J., et al., ApJ, 856, 178 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014Sci...346B.315T/abstract\">Testa, P., De Pontieu, B., Allred, J., et al., Sci, 346, 1255724 (2014)</a>"],"pubDate":"2022-08-09T08:22:45.369Z"},{"id":"pod_polito_vanessa_2022-06-20T17:06:17.013Z","submitter":"Qiangwei Cai","author":"Qiangwei Cai[1,2], Jing Ye[3,4], Hengqiang Feng[1,2], and Guoqing Zhao[1,2]","status":"published","creation-date":"2022-06-20T17:06:17.018Z","last-modified-date":"2022-09-13T01:13:33.998Z","credit":"[1] Institute of Space Physics, Luoyang Normal University, China [2] Henan Key Laboratory of Electromagnetic Transformation and Detection, Luoyang Normal University, China [3] Yunnan Observatories, Chinese Academy of Sciences, China [4] Center for Astronomical Mega-Science, Chinese Academy of Sciences, China","title":"Variations of the Plasma Environment Revealed by the Evolution of the Supra-arcade Fan in the 2017 September 10 Flare","contentBlocks":[{"type":"text","text":"It%20is%20well%20known%20that%20a%20distributed%20and%20hot%20structure%20called%20supra-arcade%20fan%20%28SAF%29%20exists%20above%20the%20post-flare%20loops%20during%20solar%20eruptions%20%28e.g.%2C%20McKenzie%20%26amp%3B%20Hudson%201999%3B%20Innes%20et%20al.%202014%29.%20The%20SAF%20is%20spatially%20consistent%20with%20various%20loop-top%20nonthermal%20emission%20sources%20%28e.g.%2C%20Gallagher%20et%20al.%202002%3B%20Reeves%20et%20al.%202020%29%2C%20implying%20that%20the%20SAF%20could%20be%20related%20to%20the%20process%20of%20particle%20acceleration.%20However%2C%20the%20plasma%20evolution%20properties%20of%20the%20SAF%20and%20roles%20of%20the%20SAF%20in%20particle%20acceleration%20are%20still%20poorly%20understood.%20Theories%20and%20numerical%20experiments%20have%20also%20pointed%20out%20the%20existence%20of%20TSs%20in%20the%20region%20above%20the%20tops%20of%20flare%20loops%20%28e.g.%2C%20Forbes%201986%29%2C%20but%20observational%20evidence%20of%20TSs%20has%20barely%20been%20found.%20Analyzing%20the%20changes%20in%20the%20spectral%20profiles%20could%20be%20a%20useful%20method%20for%20identifying%20TSs%2C%20since%20the%20sharp%20changes%20in%20temperature%2C%20density%2C%20and%20flow%20speed%20between%20the%20upstream%20and%20the%20downstream%20of%20TSs%20could%20affect%20the%20profiles%20of%20spectral%20lines%2C%20resulting%20in%20apparent%20differences%20in%20the%20intensity%2C%20Doppler%20velocity%2C%20and%20Doppler%20width."},{"type":"image","file":"","url":"nuggetvideos/2022/06/20/pod_polito_vanessa_2022-06-20T17%3A06%3A17.013Z/Figure1.jpg","hash":"c21a58282650a20d58ca69bc657a7129","mimeType":"image/jpeg","caption":"Figure%201.%20The%20imaging%20and%20spectral%20performances%20of%20the%20SAF%20observed%20by%20IRIS.%20%28a%29%20The%20IRIS%20SJI%201330%20image%20at%2016%3A07%3A58%20UT.%20%28b%29%20The%20spectrum%20of%20Fe%20XXI%201354.08%20%26Aring%3B.%20%28c%29%E2%80%93%28e%29%20The%20variations%20of%20the%20Gaussian%20fitting%20result%20of%20the%20Fe%20XXI%20line%20along%20the%20SP.%20The%20white%20dashed%20line%20in%20panel%20%28a%29%20marks%20the%20location%20of%20the%20IRIS%20slit.%20The%20black%20dashed%20line%20in%20panel%20%28b%29%20denotes%20the%20rest%20wavelength%20%CE%BB%20%3D%201354.08%20%26Aring%3B%20of%20the%20Fe%20XXI%20line.%20The%20white%20solid%20line%20called%20SP%20gives%20the%20position%20where%20the%20spectral%20profile%20is%20extracted%20to%20perform%20the%20Gaussian%20fitting.%20%28f%29%E2%80%93%28j%29%20The%20same%20as%20%28a%29%E2%80%93%28e%29%2C%20but%20at%2016%3A21%3A59%20UT."},{"type":"text","text":"Luckily%2C%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%20and%20Hinode%2FEUV%20Imaging%20Spectrometer%20%28EIS%29%20spectroscopic%20observations%20of%20the%202017%20September%2010%20flare%20%28SOL2017-09-10%29%20provide%20excellent%20spectral%20data%20and%20observational%20perspectives%20%28Figures%201%20and%202%29%2C%20enabling%20us%20to%20perform%20spectral%20diagnoses%20of%20hot%20spectral%20lines%20%28Fe%20XXI%201354.08%20%26Aring%3B%2C%20Fe%20XXIII%20263.76%20%26Aring%3B%2C%20and%20Fe%20XXIV%20255.10%20%26Aring%3B%29%20focusing%20on%20the%20SAF%20that%20exists%20at%20the%20south%20of%20the%20bright%20flare%20arcade."},{"type":"image","file":"","url":"nuggetvideos/2022/06/20/pod_polito_vanessa_2022-06-20T17%3A06%3A17.013Z/Figure2.jpg","hash":"2e38c7c8993b2fb3d1a862320e09957f","mimeType":"image/jpeg","caption":"Figure%202.%20%28a%29%20and%20%28b%29%20The%20distribution%20of%20temperature%20deduced%20from%20the%20spectral%20intensity%20of%20the%20Fe%20XXIV%20255.10%20%26Aring%3B%20and%20Fe%20XXIII%20263.76%20%26Aring%3B%20lines.%20%28c%29%20and%20%28d%29%20The%20distribution%20of%20density%20derived%20from%20the%20intensity%20of%20the%20Fe%20XXIV%20line%20and%20the%20temperature.%20The%20blue%20arrows%20in%20panel%20%28d%29%20mark%20the%20positions%20for%20calculating%20the%20change%20in%20density.%20The%20contours%20denote%20the%20shapes%20of%20SAF%20observed%20by%20the%20Fe%20XXIV%20255.10%20%26Aring%3B%20line%20%28black%20line%29%20and%20the%20Fe%20XXIII%20263.76%20%26Aring%3B%20line%20%28red%20line%29."},{"type":"text","text":"By%20calculating%20the%20IRIS%20spectral%20data%20and%20inspecting%20the%20results%2C%20Cai%20et%20al.%20%282022%29%20found%20that%20the%20intensity%20peaks%20of%20the%20Fe%20XXI%20line%20that%20is%20formed%20at%2010%20MK%20basically%20correspond%20to%20the%20valley%20of%20the%20Doppler%20velocity%20and%20Doppler%20width%20%28Figure%201%3B%20and%20also%20in%20results%20of%20Fe%20XXIII%20and%20Fe%20XXIV%20lines%2C%20which%20are%20not%20shown%29.%20Meanwhile%2C%20the%20temperature%20derived%20from%20the%20Fe%20XXIV%20and%20Fe%20XXIII%20lines%20and%20the%20density%20derived%20from%20the%20intensity%20of%20the%20Fe%20XXIV%20line%20both%20increase%20on%20the%20upper%20side%20of%20the%20SAF%20%28Figure%202%29.%20The%20change%20ratio%20of%20the%20density%20at%20the%20positions%20marked%20by%20the%20blue%20arrows%20in%20Figure%202%28d%29%20is%20about%203.9.%20These%20results%20demonstrate%20the%20complexity%20of%20the%20SAF%20in%20dynamical%20and%20thermal%20evolutions%20and%20the%20possible%20existence%20of%20a%20compressed%20interface%20in%20the%20SAF."},{"type":"image","file":"","url":"nuggetvideos/2022/06/20/pod_polito_vanessa_2022-06-20T17%3A06%3A17.013Z/Figure3.jpg","hash":"85d6bb063a6b67d28358d6fb9ed7ca28","mimeType":"image/jpeg","caption":"Figure%203.%20The%20results%20of%20numerical%20experiments%20and%20the%20synthetic%20spectrum.%20%28a%29%20The%20distribution%20of%20the%20electron%20density%20around%20the%20SAF.%20%28b%29%20The%20contours%20of%20the%20Mach%20numbers%20overlaid%20on%20the%20image%20of%20the%20divergence%20of%20velocity.%20%28c%29%20The%20synthetic%20Fe%20XXI%201354.08%20%26Aring%3B%20spectrum.%20%28d%29%E2%80%93%28f%29%20The%20variations%20of%20the%20Gaussian%20fitting%20result%20for%20the%20Fe%20XXI%20line%20along%20the%20SP.%20The%20dashed%20lines%20in%20panels%20%28b%29%20and%20%28c%29%20separate%20the%20region%20into%20the%20upstream%20and%20the%20downstream.%20The%20dashed%20lines%20in%20panels%20%28b%29%20and%20%28c%29%20and%20the%20solid%20lines%20in%20panels%20%28d%29%E2%80%93%28f%29%20mark%20the%20same%20positions.%20One%20pixel%20corresponds%20to%20156%20km."},{"type":"text","text":"Based%20on%20the%20results%20of%20numerical%20experiments%2C%20we%20estimated%20the%20synthetic%20emission%20of%20the%20Fe%20XXI%20line%20to%20study%20the%20candidate%20mechanism%20for%20producing%20the%20distribution%20of%20the%20spectral%20parameters%20%28Figure%203%29.%20At%20the%20locations%20where%20TSs%20exist%2C%20the%20intensity%20of%20the%20Fe%20XXI%20line%20rapidly%20increases%20due%20to%20the%20compression%20of%20the%20plasma.%20The%20Doppler%20velocity%20and%20the%20Doppler%20width%20both%20show%20a%20descend%E2%80%93ascent%20trend%20where%20the%20intensity%20peaks%2C%20which%20resembles%20the%20results%20of%20the%20observations%20shown%20in%20Figure%201.%20Comparing%20the%20observational%20results%20with%20the%20synthetic%20spectral%20profiles%2C%20Cai%20et%20al.%20%282022%29%20realized%20that%20the%20TSs%20existing%20above%20the%20tops%20of%20the%20flare%20loops%20are%20candidates%20for%20the%20production%20of%20the%20interface."},{"type":"text","text":"In%20addition%2C%20the%20height%20and%20velocity%20of%20the%20RHESSI%20HXR%20source%20at%20the%20cusp%20region%20and%20that%20of%20the%20SAF%20are%20similar%2C%20indicating%20that%20the%20SAF%20is%20related%20to%20the%20formation%20of%20the%20HXR%2C%20possibly%20offering%20a%20cradle%20of%20a%20hot%20and%20dense%20plasma%20environment%20in%20the%20process%20of%20particle%20acceleration.%20The%20SAF%20shows%20discontinuous%20property%20during%20the%20rising%20process%2C%20which%20could%20be%20caused%20by%20the%20nonuniform%20process%20of%20the%20magnetic%20reconnection%20and%20the%20occurrence%20of%20tearing%20mode%20instability%20in%20solar%20eruptions.%20The%20relative%20change%20in%20position%20of%20the%20SAF%20and%20the%20post-flare%20loops%20confirms%20the%20conclusion%20that%20the%20post-flare%20loops%20are%20caused%20by%20the%20shrinkage%20of%20the%20higher%20magnetic%20arcade%20in%20the%20SAF%20%28Forbes%20%26amp%3B%20Acton%201996%3B%20Lin%202004%29."},{"type":"image","file":"","url":"nuggetvideos/2022/06/20/pod_polito_vanessa_2022-06-20T17%3A06%3A17.013Z/Figure4.jpg","hash":"dffcf5ad6ab9c5a2fa4364c4c31fb4db","mimeType":"image/jpeg","caption":"Figure%204.%20%28a%29%20The%20local%20image%20of%20the%20IRIS%20SJI%201330%20at%2016%3A04%20UT.%20The%20vertical%20lines%20A%20and%20B%20denote%20the%20positions%20where%20the%20emission%20intensity%20was%20extracted%20to%20create%20the%20spacetime%20maps.%20%28b%29%20and%20%28c%29%20The%20corresponding%20spacetime%20maps%20obtained%20at%20positions%20A%20and%20B%2C%20respectively.%20%28d%29%20and%20%28e%29%20Enlargements%20of%20the%20spacetime%20maps%20in%20the%20black%20boxes."},{"type":"text","text":"In%20view%20of%20the%20fact%20that%20the%20height%20of%20the%20SAF%20is%20close%20to%20the%20hard%20X-ray%20source%2C%20we%20conclude%20that%20the%20compressed%20interface%20could%20be%20related%20to%20TSs%2C%20taking%20into%20account%20the%20synthetic%20spectral%20profiles%20obtained%20from%20numerical%20experiments%20for%202D%20flare%20models.%20In%20turn%2C%20the%20variations%20of%20the%20spectral%20profiles%20might%20be%20useful%20tools%20for%20identifying%20TSs%20from%20%28E%29UV%20spectral%20observations.%20This%20study%20provides%20both%20observational%20and%20theorical%20evidences%20that%20the%20interface%20related%20to%20TSs%20might%20be%20detected%20by%20%28E%29UV%20observations%20in%20the%20future.%0A%0AFor%20the%20full%20paper%2C%20please%20check%20out%20Cai%20et%20al.%20%282022%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1999ApJ...519L..93M/abstract\">McKenzie, D. E. , & Hudson, H. S., ApJL, 519, 93 (1999)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014ApJ...796...27I/abstract\">Innes, D. E. et al., ApJ, 796, 27 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2002SoPh..210..341G/abstract\">Gallagher, P. T. et al., SoPh, 210, 341 (2002)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...905..165R/abstract\">Reeves, K. K. et al., ApJ, 905, 165 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1986ApJ...305..553F/abstract\">Forbes, T. G., ApJ, 305, 553 (1986)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022ApJ...929...99C/abstract\">Cai, Q. W. et al., ApJ, 929, 99 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1996ApJ...459..330F/abstract\">Forbes, T. G., & Acton, L. W., ApJ, 459, 330 (1996)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2004SoPh..222..115L/abstract\">Lin, J., SoPh, 222, 115 (2004)</a>","",""],"pubDate":"2022-06-20T01:09:37.667Z"},{"id":"pod_polito_vanessa_2022-05-26T17:47:04.706Z","submitter":"Andrew Hillier","author":"Andrew Hillier[1] & Vanessa Polito[2,3]","status":"published","creation-date":"2022-05-26T17:47:04.736Z","last-modified-date":"2022-06-14T17:04:29.93Z","credit":"[1] CEMPS, University of Exeter, Exeter EX4 4QF U.K, [2] Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA 94035, USA, [3] Lockheed Martin Solar & Astrophysics Laboratory, Org. A021S, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304, USA","title":"IRIS observations of bi-directional jets in a prominence as signatures of magnetic reconnection","contentBlocks":[{"type":"text","text":"Space-based%20observations%20of%20quiescent%20prominences%20in%20cool%20spectral%20lines%2C%20including%20those%20by%20IRIS%2C%20show%20that%20many%20of%20these%20prominences%20are%20highly%20dynamic%2C%20with%20observations%20showing%20transonic%20downflows%20%28Chae%202010%29%20and%20instabilities%20%28Berger%20et%20al%202010%29.%20There%20are%20a%20number%20of%20instances%20where%20magnetic%20reconnection%20of%20the%20prominence%20magnetic%20field%20has%20been%20invoked%20to%20explain%20how%20flows%20are%20being%20driven%20%28e.g.%20Chae%202010%2C%20Hillier%20et%20al%202011%29.%20However%2C%20clear%20evidence%20that%20the%20internal%20magnetic%20fields%20of%20a%20prominence%20can%20become%20sufficiently%20stressed%20to%20then%20reconnect%20and%20drive%20flows%20has%20proved%20elusive.%20It%20is%20exactly%20this%20evidence%20that%20has%20been%20found%20in%20IRIS%20prominence%20observations."},{"type":"image","file":"","url":"nuggetvideos/2022/05/26/pod_polito_vanessa_2022-05-26T17%3A47%3A04.706Z/Figure1a.png","hash":"aa79b92f4ad62b247e40745bb4e6e3f8","mimeType":"image/png","caption":"Figure%201.%20Quiescent%20prominence%20observed%20by%20IRIS%20on%20the%20South-East%20limb%20of%20the%20Sun%20in%20the%20Mg%20II%20k%20line.%20Region%20shown%20in%20the%20left%20panel%20of%20Figure%202%20highlighted%20by%20the%20yellow%20box."},{"type":"text","text":"A%20quiescent%20prominence%20%28shown%20in%20Figure%201%29%20was%20observed%20with%20IRIS%20on%20the%20South-East%20limb%20of%20the%20Sun%20on%20June%2030%2C%202015%20between%206%3A57%20UT%20and%2011%3A20%20UT.%20This%20prominence%20presented%20many%20interesting%20dynamic%20features%20including%20multiple%20downflows%20and%20upflows%20%28e.g.%20see%20Hillier%20%26amp%3B%20Polito%202018%29.%20In%20these%20observations%20one%20particular%20interesting%20phenomenon%20could%20be%20observed%3A%20the%20formation%20of%20bi-directional%20jets%20of%20prominence%20material%20%28Hillier%20%26amp%3B%20Polito%202021%29."},{"type":"image","file":"","url":"nuggetvideos/2022/05/26/pod_polito_vanessa_2022-05-26T17%3A47%3A04.706Z/Figure2_nugget.jpg","hash":"8b81085e70df4a362a5681a5c81f1411","mimeType":"image/jpeg","caption":"Figure%202.%20Body%20of%20the%20prominence%20as%20observed%20in%20MgII%20k%20%28left-hand%20panels%29.%20The%20right-hand%20panels%20show%20the%20temporal%20evolution%20in%20the%20white%20box%20in%20the%20left%20panel.%20Motion%20of%20blobs%20along%20the%20plasma%20sheet%20is%20tracked%20by%20the%20arrows."},{"type":"text","text":"What%20separates%20these%20jets%20from%20all%20the%20other%20prominence%20flows%20that%20have%20been%20previously%20reported%20is%20that%20they%20are%20bi-directional.%20By%20this%20we%20mean%20that%20from%20a%20single%20local%20point%2C%20material%20is%20observed%20to%20be%20ejected%20at%20speeds%20up%20to%2010%20km%2Fs%20in%20two%20opposite%20directions.%20These%20ejections%20formed%20in%20regions%20where%20long%20plasma%20sheets%20developed%2C%20and%20were%20composed%20of%20multiple%20plasma%20blobs.%20We%20observe%20flows%20bringing%20material%20into%20some%20of%20these%20jets%20as%20well%20as%20the%20outward%20ejections%2C%20and%20even%20in%20one%20case%20the%20late%20evolution%20of%20the%20jet%20appears%20to%20show%20the%20presence%20of%20flow-driven%20instabilities%20similar%20to%20those%20observed%20by%20Hillier%20%26amp%3B%20Polito%202018.%20The%20observations%20here%20present%20all%20the%20hall-marks%20of%20jets%20driven%20by%20magnetic%20reconnection%2C%20i.e.%20a%20current%20sheet%20%28the%20observed%20plasma%20sheet%29%20developing%20magnetic%20reconnection%20producing%20reconnection%20jets%20%28the%20observed%20bi-directional%20jets%29.%20%0A%0AUnderstanding%20that%20these%20jets%20can%20be%20created%20by%20magnetic%20reconnection%20means%20we%20can%20learn%20something%20about%20the%20prominence%20environment.%20For%20example%20the%20intensity%20of%20the%20current%20sheet%20suggests%20a%20prominence%20magnetic%20field%20of%204.5%20G%20to%209.2%20G%20with%20the%20reconnected%20component%20of%20the%20magnetic%20field%20around%201%20G%20needed%20to%20explain%20the%20speed%20of%20the%20ejections.%20Some%20open%20questions%20remain%20though.%20Are%20the%20blobs%20that%20are%20being%20emitted%20plasmoids%20creating%20by%20tearing%20of%20the%20current%20sheet%3F%20If%20they%20are%20then%20the%20size%20of%20the%20blobs%20doesn%E2%80%99t%20scale%20as%20expected%20with%20the%20observed%20thickness%20of%20the%20current%20sheet.%20If%20these%20are%20not%20plasmoids%20created%20by%20current-sheet%20tearing%20then%20it%20opens%20up%20other%20possibilities%2C%20for%20example%20that%20they%20are%20observations%20of%20slow-mode%20shocks%20created%20by%20the%20reconnection.%20%0A%0AIn%20this%20article%20we%20have%20presented%20evidence%2C%20in%20the%20form%20of%20observations%20of%20bursty%20bi-directional%20jet%20formation%2C%20that%20reconnection%20of%20the%20internal%20magnetic%20field%20of%20a%20quiescent%20prominence%20can%20occur.%20With%20so%20many%20fantastic%20observations%20of%20prominences%20in%20the%20IRIS%20archive%20it%20is%20likely%20that%20many%20more%20of%20these%20events%20can%20be%20found."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2010ApJ...716.1288B/abstract\">Berger, T. E., Slater, G., Hurlburt, N., et al. 2010, ApJ, 716, 1288</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2010ApJ...714..618C/abstract\">Chae, J. 2010, ApJ, 714, 618</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2011PASJ...63L..19H/abstract\">Hillier, A., Isobe, H., & Watanabe, H. 2011, PASJ, 63, 19</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...864L..10H/abstract\">Hillier, A., & Polito, V. 2018, ApJ, 864, L10</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...651A..60H/abstract\">Hillier, A., & Polito, V. 2021, A&A, 651, A60</a>","","","","",""],"pubDate":"2022-06-14T17:04:53.571Z"},{"id":"pod_polito_vanessa_2022-04-19T21:30:38.175Z","submitter":"Souvik Bose (*now at Lockheed Martin Solar & Astrophysics Laboratory)","author":"Souvik Bose[1,2]*, Luc Rouppe van der Voort [1,2], Jayant Joshi[1,2], Vasco M.J. Henriques[1,2], Daniel Nobrega-Siverio[3,4,1,2], Juan Martinez-Sykora[5,6,1,2] and Bart De Pontieu[5,1,2]","status":"published","creation-date":"2022-04-19T21:30:38.178Z","last-modified-date":"2022-05-12T18:22:56.201Z","credit":"[1] Institute of Theoretical Astrophysics, Oslo, Norway [2] Rosseland Centre for Solar Physics, Oslo, Norway [3] Instituto de Astrofisica de Canarias, Tenerife, Spain [4] Departamento de Astrofisica, Universidad de La Laguna, Spain [5] Lockheed Martin Solar and Astrophysics Laboratory, USA [6] Bay Area Environmental Research Institute, USA","title":"Evidence of the multi-thermal nature of spicular downflows","contentBlocks":[{"type":"text","text":"Spectroscopic%20observations%20of%20the%20emission%20lines%20formed%20in%20the%20solar%20transition%20region%20%28TR%29%20commonly%20show%20persistent%20redshifts%20on%20the%20order%20of%2010--15%20km%2Fs.%20These%20redshifts%20%28also%20interpreted%20as%20downward%20mass%20flows%29%20have%20been%20the%20subject%20of%20interest%20for%20many%20decades%20ever%20since%20the%20launch%20of%20NASA%E2%80%99s%20Skylab%20mission%20in%20the%20seventies.%20Several%20theories%2C%20such%20as%20downward%20propagating%20acoustic%20waves%20generated%20by%20nanoflares%20in%20the%20corona%20%28Hansteen%201993%29%2C%20the%20%26quot%3Breturn%26quot%3B%20of%20the%20previously%20heated%20spicular%20material%20%28Pneuman%20%26amp%3B%20Kopp%201977%3B%20McIntosh%20et%20al.%202012%29%2C%20and%20rapid%20episodic%20heating%20at%20the%20base%20of%20the%20corona%20%28Hansteen%20et%20al.%202010%29%2C%20have%20been%20proposed%20in%20the%20past%2C%20but%20no%20definitive%20consensus%20has%20emerged%20so%20far.%0A%0AThe%20present%20study%20aims%20to%20better%20understand%20the%20cause%20of%20such%20downflows%20by%20studying%20the%20coronal%20and%20TR%20responses%20to%20the%20recently%20reported%20chromospheric%20spicular%20downflows%20%28referred%20to%20as%20downflowing%20rapid%20redshifted%20excursions%20%28RREs%29%20in%20Bose%20et%20al.%202021a%29%20and%20their%20impact%20on%20the%20heating%20of%20the%20solar%20atmosphere.%20Since%20the%20average%20upward%20mass%20flux%20carried%20by%20the%20ubiquitous%20spicules%20is%20roughly%20100%20times%20more%20than%20what%20is%20needed%20to%20contribute%20to%20the%20solar%20wind%2C%20it%20is%20highly%20likely%20that%20the%20remaining%20heated%20spicular%20plasma%20undergoes%20cooling%20and%20is%20eventually%20drained%20back%20to%20the%20chromosphere%20via%20the%20TR%20%28Pneuman%20%26amp%3B%20Kopp%201977%29."},{"type":"image","file":"","url":"nuggetvideos/2022/04/19/pod_polito_vanessa_2022-04-19T21%3A30%3A38.175Z/Screenshot 2022-05-11 at 12.38.53.png","hash":"db40d62b8872d950208b59c8635693d0","mimeType":"image/png","caption":"Figure%201%3A%20Top%20row%20shows%20an%20overview%20of%20the%20coordinated%20observations%20of%20the%20two%20%28enhanced%20network%20and%20quiet-Sun%29%20targets%20with%20SST%2C%20IRIS%2C%20and%20SDO.%20The%20bottom%20row%20shows%20an%20overview%20of%20the%20MHD%20simulation%20snapshot%20at%20a%20given%20instant%20with%202D%20slices%20of%20temperature%20and%20vertical%20velocity.%20The%20spicules%20marked%20as%201%20and%202%20are%20analyzed%20in%20detail%20in%20Fig.%204."},{"type":"text","text":"We%20have%20used%20two%20sets%20of%20coordinated%20high-resolution%2C%20multi-wavelength%20observations%20from%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%2C%20the%20Swedish%201-m%20Solar%20Telescope%20%28SST%2C%20Scharmer%20et%20al.%202003%29%2C%20and%20the%20Solar%20Dynamics%20Observatory%20%28SDO%2C%20Pesnell%20et%20al.%202012%29%20focusing%20on%20an%20enhanced%20network%20and%20quiet-Sun%20target%20close%20to%20the%20disc-center%2C%20along%20with%20an%20advanced%202.5D%20MHD%20simulation%20of%20spicules%20%28Mart%26iacute%3Bnez-Sykora%20et%20al.%202017%29%20for%20this%20study.%20Figure%201%20shows%20an%20overview%20of%20the%20observations%20and%20the%20numerical%20simulation.%0A%0AAmple%20occurrences%20of%20spicular%20downflows%20were%20found%20in%20both%20the%20datasets%20and%20several%20examples%20focusing%20on%20their%20spatio-temporal%20evolution%20across%20multiple%20wavelengths%2C%20ranging%20from%20the%20cooler%20chromospheric%20to%20the%20hotter%20coronal%20channels%2C%20were%20shown%20in%20this%20study%20%28Bose%20et%20al.%202021b%29%2C%20which%20exemplified%20the%20multi-thermal%20nature%20associated%20with%20such%20downflows.%20One%20such%20example%20is%20shown%20in%20Fig.%202%20below%20which%20clearly%20shows%20the%20spatio-temporal%20evolution%20of%20a%20downflowing%20RRE%20in%20all%20three%20%28IRIS%2C%20SST%2C%20and%20SDO%29%20instruments%20including%20their%20spectral%20signatures.%20The%20X-t%20maps%20shown%20in%20the%20top%20row%20of%20Fig.%202%20exemplify%20the%20evolution%20of%20the%20spicule%20in%20the%20different%20wavelength%20channels%2C%20while%20the%20middle%20row%20clearly%20shows%20redward%20excursion%20asymmetry%20associated%20with%20this%20event%20in%20H-%5Cbegin%7Bequation%7D%5Calpha%5Cend%7Bequation%7D%2C%20Ca%20II%20K%2C%20Si%20IV%2C%20and%20Mg%20II%20k%20spectral%20lines.%20The%20apparent%20downward%20motion%20in%20the%20X-t%20maps%20in%20tandem%20with%20the%20co-temporal%20redward%20excursion%20asymmetry%20across%20multiple%20spectra%20suggests%20that%20these%20redshfits%20are%20associated%20with%20real%20mass%20flows%20that%20are%20truly%20multi-thermal%20in%20nature.%20Moreover%2C%20the%20magnitude%20of%20the%20Doppler%20shifts%20of%20the%20TR%20spectra%20are%20close%20to%20the%20average%20redshifts%20observed%20in%20this%20region%2C%20which%20further%20implies%20that%20these%20flows%20could%20be%20responsible%20for%20the%20persistent%20downflows%20that%20have%20been%20observed%20for%20several%20decades."},{"type":"image","file":"","url":"nuggetvideos/2022/04/19/pod_polito_vanessa_2022-04-19T21%3A30%3A38.175Z/Screenshot 2022-05-11 at 13.33.53.png","hash":"bd0bc0612f1d6e2a16ba1d8f704d8468","mimeType":"image/png","caption":"Figure%202%3A%20A%20representative%20example%20of%20a%20spicular%20downflow%20and%20its%20signatures%20across%20multiple%20wavelength%20channels.%20The%20top%20row%20%28left%20to%20right%29%20shows%20the%20downflowing%20RRE%20in%20the%20H-%24%5Calpha%24%20red%20wing%2C%20followed%20by%20its%20spatio-temporal%20evolution%20%28X-t%20maps%29%20in%20different%20wavelength%20channels.%20Middle%20row%20%28left%20to%20right%29%20shows%20spectral-time%20slices%20in%20H-%5Cbegin%7Bequation%7D%5Calpha%5Cend%7Bequation%7D%2C%20Ca%20II%20K%2C%20Si%20IV%2C%20and%20Mg%20II%20k%20corresponding%20to%20the%20downflowing%20RRE%20in%20the%20top%20row.%20Bottom%20row%20%28left%20to%20right%29%3A%20corresponding%20spectral%20profiles%20for%20the%20different%20wavelengths%20at%20the%20instant%20of%20maximum%20redward%20excursion%20%28indicated%20by%20the%20magenta%20marker%20in%20the%20middle%20row%29."},{"type":"text","text":"The%20downflows%20reported%20in%20this%20study%20are%20very%20likely%20associated%20with%20the%20draining%20phases%20of%20the%20previously%20heated%20spicular%20plasma%20as%20suggested%20by%20Pneumann%20%26amp%3B%20Kopp%20%281977%29%20and%20McIntosh%20et%20al.%20%282012%29.%20However%2C%20unlike%20any%20of%20the%20earlier%20studies%2C%20we%20present%20unambiguous%20evidence%20of%20the%20connection%20between%20spicules%20and%20their%20association%20with%20TR%20redshifts.%20Moreover%2C%20with%20the%20help%20of%20the%20MHD%20simulation%2C%20we%20proposed%20two%20mechanisms%20--%20%28i%29%20co-spatial%20spicular%20upflow%20followed%20by%20a%20downflow%20and%20%28ii%29%20downflows%20along%20a%20loop%2C%20that%20explain%20their%20ubiquitous%20nature.%20Both%20scenarios%20are%20presented%20in%20Fig.%203%20along%20with%20their%20synthetic%20spectral%20signatures%20that%20agree%20very%20well%20with%20the%20observations."},{"type":"image","file":"","url":"nuggetvideos/2022/04/19/pod_polito_vanessa_2022-04-19T21%3A30%3A38.175Z/Screenshot 2022-05-11 at 14.06.38.png","hash":"7e4bc0ec5d7bdac59090e223a72b84ea","mimeType":"image/png","caption":"Figure%203%3A%20Possible%20spicular%20downflowing%20scenarios%20in%20the%20MHD%20simulation.%20Top%20row%3A%20co-spatial%20upflows%20and%20downflows%20along%20with%20the%20synthesized%20Ca%20II%20K%2C%20Mg%20II%20k%20and%20Si%20IV%20spectral%20lines%3B%20bottom%20row%3A%20downflows%20along%20a%20loop%20with%20synthetic%20spectral-time%20slices%20of%20Ca%20II%20K%2C%20Mg%20II%20k%20and%20Si%20IV."},{"type":"text","text":"The%20bottom%20row%20of%20Fig.%202%20suggests%20that%20the%20observed%20Ca%20II%20K%2C%20Si%20IV%2C%20and%20Mg%20II%20k%20spectral%20profiles%20associated%20with%20the%20spicular%20downflow%20show%20an%20enhancement%20in%20their%20observed%20intensities%20compared%20to%20the%20average%20%28background%29.%20Similar%20behavior%20was%20also%20found%20in%20the%20simulations%20where%20the%20synthetic%20intensities%20corresponding%20to%20the%20above%20set%20of%20spectral%20lines%20show%20an%20enhancement%20in%20comparison%20to%20the%20upflowing%20counterparts%20%28see%20Fig.%203%20top%20row%29.%20Analysis%20of%20various%20physical%20parameters%20derived%20from%20the%20numerical%20simulation%20led%20to%20the%20conclusion%20that%20downflowing%20phases%20of%20spicules%20have%20enhanced%20heating%20%28due%20to%20ambipolar%20diffusion%20effects%29%20which%20in%20turn%20increases%20the%20temperature%20by%202000--3000%20K.%20The%20analysis%20is%20detailed%20in%20Fig.%204."},{"type":"image","file":"","url":"nuggetvideos/2022/04/19/pod_polito_vanessa_2022-04-19T21%3A30%3A38.175Z/Screenshot 2022-05-11 at 14.42.22.png","hash":"a7ea6aae69151c23745843404844d6bd","mimeType":"image/png","caption":"Figure%204%3A%20Enhanced%20heating%20associated%20with%20the%20downflowing%20stages%20of%20spicules.%20Panel%20%28a%29%20shows%202D%20slices%20and%20space-time%20evolution%20of%20the%20indicated%20physical%20parameters%20derived%20from%20the%20MHD%20simulation%20for%20spicule%201%20whereas%20panel%20%28b%29%20shows%20the%20same%20parameters%20in%20the%20same%20format%20for%20spicule%202.%20Both%20spicules%201%20and%202%20are%20indicated%20in%20the%20bottom%20row%20of%20Fig.%201."},{"type":"text","text":"The%20current%20work%20builds%20upon%20the%20previous%20studies%20%28Pneumann%20%26amp%3B%20Kopp%201977%3B%20McIntosh%20et%20al.%202012%29%20but%20more%20importantly%20provides%20a%20compelling%20scenario%20that%20unambiguously%20links%20the%20persistent%20redshifts%20observed%20in%20the%20TR%20with%20spicules.%20The%20downflows%20are%20most%20likely%20the%20aftermath%20of%20the%20previously%20heated%20spicular%20material%20that%20underwent%20cooling.%20A%20detailed%20comparison%20with%20an%20MHD%20simulation%20also%20provides%20strong%20theoretical%20support%20to%20our%20interpretation%20which%20highlights%20the%20multi-thermal%20nature%20of%20spicular%20downflows.%20Further%20coordinated%20studies%20are%20needed%20to%20quantify%20what%20fraction%20of%20the%20TR%20redshifts%20are%20related%20to%20chromospheric%20spicules."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1993ApJ...402..741H/abstract\">Hansteen, Viggo, ApJ 402, 741 (1993)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1977A%26A....55..305P/abstract\">Pneuman, G. W. ; Kopp, R. A., A&A 55, 305 (1977)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...654A..51B/abstract\">Bose, Souvik et al., A&A 654, 51 (2021b)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2012ApJ...749...60M/abstract\">McIntosh, Scott W. et al., ApJ 749, 60 (2012)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2010ApJ...718.1070H/abstractt\">Hansteen, Viggo et al. ApJ 782, 2 (2010)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...647A.147B/abstract\">Bose, Souvik et al., A&A 647, 147 (2021a)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017Sci...356.1269M/abstract\">Martínez-Sykora, J et al., Science 356, 6344 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu, B. et al. SoPh 289, 7 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2003SPIE.4853..341S/abstract\">Scharmer, Goran B. et al. SPIE 4853, 341 (2003)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2012SoPh..275....3P/abstract\">Pesnell, W. Dean et al., SoPh 275, 3 (2012)</a>"],"pubDate":"2022-05-12T18:23:04.145Z"},{"id":"pod_polito_vanessa_2022-03-22T16:10:52.903Z","submitter":"","author":"Hechao Chen[1], Hui Tian[1,2], Leping Li[2], Hardi Peter[3], Lakshmi Pradeep Chitta[3], Zhenyong Hou[1]","status":"published","creation-date":"2022-03-22T16:10:52.906Z","last-modified-date":"2022-04-07T17:23:25.293Z","credit":"[1] School of Earth and Space Sciences, Peking University, China. [2] CAS, National Astronomical Observatories, China. [3] Max Planck Institute for Solar System Research, Germany","title":"Coronal condensation as the source of quasi-steady supersonic downflows into sunspots","contentBlocks":[{"type":"text","text":"In%20the%201980s%2C%20downflows%20at%20supersonic%20speeds%20towards%20sunspots%20were%20discovered%20in%20the%20transition%20region%20%28TR%29%20spectra.%20With%20the%20launch%20of%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%2C%20a%20wealth%20of%20observational%20data%20of%20sunspots%20at%20high%20spatial%20and%20spectral%20resolutions%20have%20revealed%20that%20these%20TR%20supersonic%20downflows%20%28SDs%29%20commonly%20exist%20above%20the%20majority%20of%20sunspots%20%28Samanta%20et%20al.%202018%29.%20In%20IRIS%20spectra%2C%20they%20are%20often%20observed%20as%20strongly%20redshifted%20secondary%20emission%20peaks%20with%20a%20speed%20of%20%7E100%20km%2Fs%20and%20last%20for%20at%20least%20several%20hours%20%28e.g.%3B%20Tian%20et%20al.%202014%3B%20Straus%20et%20al.%202015%3B%20Chitta%20et%20al.%202016%29%20%28See%20Figure%201%29.%20However%2C%20how%20these%20long-lived%20supersonic%20downflows%20form%20and%20what%20mechanisms%20are%20responsible%20for%20the%20substantial%20and%20stable%20mass%20supply%20has%20remained%20unclear%20for%20the%20past%20four%20decades."},{"type":"image","file":"","url":"nuggetvideos/2022/03/22/pod_polito_vanessa_2022-03-22T16%3A10%3A52.903Z/iris0_ok.png","hash":"71f63b3da527206cf4af36f11863e9ae","mimeType":"image/png","caption":"Figure%201.%20IRIS%20observations%20of%20sunspot%20supersonic%20downflows%20%28SDs%29.%20%28a%29%20Image%20of%20an%20IRIS%20raster%20scan%20at%20Mg%20II%20k%202803.43%20%26Aring%3B.%20Coronal%20rain%20flows%20into%20the%20sunspot%20along%20the%20yellow%20arrow.%20%28b%29%20Spatial%20extent%20of%20SDs%20as%20shown%20the%20intensity%20images%20of%20the%20secondary%20component%20of%20Si%20IV%201400%20%26Aring%3B%20integrated%20in%20the%20velocity%20range%20of%2050%20km%2Fs%20to%20300%20km%2Fs%20.%20%28c%29%20Average%20spectrum%20in%20the%20small%20red%20box%20%283%E2%80%B2%E2%80%B2%20%26times%3B%203%E2%80%B2%E2%80%B2%20%29%20shown%20in%20panel%20b%20%28Raster%202%29.%20A%20six-component%20Gaussian%20fit%20to%20the%20spectrum%20is%20shown%20as%20the%20red%20%28primary%20component%29%20and%20blue%20lines%20%28secondary%20component%29."},{"type":"text","text":"With%20joint%20observations%20from%20IRIS%20and%20several%20other%20telescopes%20at%20multiple%20vantage%20points%2C%20Chen%20et%20al.%20%282022%29%20have%20recently%20investigated%20a%20series%20of%20TR%20SDs%20in%20NOAA%20AR%2012740%20%28see%20Figure%201%29%20and%20their%20associated%20coronal%20dynamic%20processes.%20They%20clearly%20tracked%20the%20formation%20of%20a%20quasi-steady%20SD%20event%20for%20the%20first%20time.%20Dual-perspective%20EUV%20imaging%20observations%20%28see%20Figures%202%20and%203%29%20reveal%20that%20these%20downflows%20originate%20from%20the%20cooling%20and%20condensation%20of%20hot%20coronal%20plasma%20at%20magnetic%20dips%20along%20a%20large-scale%20closed%20magnetic%20loop%20system%20spanning%20the%20sunspot%20region%20and%20a%20remote%20region.%20In%20the%20magnetic%20dip%20region%2C%20repeated%20coronal%20rain%20forms%20and%20continuously%20flows%20along%20these%20magnetic%20loops%20towards%20the%20sunspot%2C%20resulting%20in%20a%20TR%20SD%20event."},{"type":"image","file":"","url":"nuggetvideos/2022/03/22/pod_polito_vanessa_2022-03-22T16%3A10%3A52.903Z/2.png","hash":"4317af89bc409c511c4510b49aa96726","mimeType":"image/png","caption":"Figure%202.%20Quasi-steady%20supersonic%20downflows%20%28SDs%29%20resulting%20from%20a%20long-lived%20coronal%20rain%20event.%20%28a%29%20An%20IRIS%20SJI%201400%20%26Aring%3B%20image.%20SDs%20were%20best%20detected%20at%20the%20last%20slit%20position%20%28the%20black%20line%29.%20%28b1%29-%28b3%29%20Temporal%20evolution%20of%20the%20Si%20IV%201403%20%26Aring%3B%2C%20O%20IV%201401%20%26Aring%3B%2C%20and%20Mg%20II%202796%20%26Aring%3B%20line%20profiles%20averaged%20within%20the%20section%20marked%20by%20the%20green%20line%20shown%20in%20%28a%29.%20%28c%29%20The%20corresponding%20coronal%20rain%20event%20in%20an%20EUVI%20304%20%26Aring%3B%20image%20from%20a%20different%20perspective.%20The%20%28magnetic%29%20dip%20region%20is%20marked%20by%20the%20blue%20%26quot%3B%2B%26quot%3B%20sign.%20%28d%29%20Space-time%20diagram%20of%20EUVI%20304%20%26Aring%3B%20intensity%20for%20the%20trajectory%20%60%60S1%26quot%3B%20shown%20in%20panel%20%28c%29.%20The%20period%20of%20the%20IRIS%20four-step%20rasters%20is%20marked%20by%20the%20green%20solid%20line%20at%20the%20bottom.%20In%20%28a%29%20and%20%28c%29%2C%20the%20cyan%20plus%20signs%20mark%20the%20same%20heliocentric%20position%20after%20considering%20the%20solar%20rotation%2C%20and%20the%20yellow%20dashed%20line%20indicates%20the%20same%20altitude."},{"type":"text","text":"Based%20on%20imaging%20observations%20and%20magnetic%20field%20extrapolations%2C%20the%20authors%20proposed%20a%20reconnection-facilitated%20coronal%20condensation%20scenario%20%28see%20Figure%203b%20and%20also%20Li%20et%20al.%202018%29.%20In%20this%20scenario%2C%20the%20magnetic%20dips%20form%20slowly%20via%20reconnection%20of%20opposite-polarity%20coronal%20loops.%20With%20the%20presence%20of%20this%20dip%20region%2C%20the%20hot%20coronal%20plasma%20soon%20cools%20and%20condenses%20via%20thermal%20instability.%20In%20this%20process%2C%20condensed%20materials%20soon%20accumulate%20as%20a%20transient%20prominence%20in%20the%20dip%20region%20and%20thus%20form%20a%20mass%20reservoir%20available%20to%20feed%20a%20long-lasting%20rain%20flow.%20As%20the%20rain%20persistently%20drains%20into%20the%20sunspot%20along%20different%20trajectories%20in%20funnel-like%20magnetic%20structures%20%28sunspot%20plumes%29%2C%20the%20funnel%20effect%20of%20this%20magnetic%20geometry%20further%20reshapes%20the%20clumpy%20rain%20at%20the%20coronal%20height%20into%20a%20more%20elongated%20and%20stream-like%20one%20when%20reaching%20the%20lower%20atmosphere.%20This%20thus%20leads%20to%20the%20quasi-steady%20SDs."},{"type":"image","file":"","url":"nuggetvideos/2022/03/22/pod_polito_vanessa_2022-03-22T16%3A10%3A52.903Z/new2.png","hash":"2761b6d4ae68b9c5f9bdc086a23bc63e","mimeType":"image/png","caption":"Figure%203.%20Global%20view%20of%20coronal%20rain%2Fprominence%20activity%20and%20supersonic%20downflows%20%28SDs%29%20near%20the%20sunspot%20observed%20by%20STEREO-A%2FEUVI.%20%28a%29%20rotated%20171%20%26Aring%3B%20and%20304%20%26Aring%3B%20images.%20%28b%29%20a%20possible%20scenario%20for%20the%20formation%20of%20reconnection-facilitated%20coronal%20condensation%20and%20its%20induced%20quasi-steady%20SDs.%20%28c%29%20Magnetic%20dips%20reconstructed%20by%20the%20PFSS%20model."},{"type":"text","text":"The%20drainage%20of%20coronal%20rain%20and%20its%20resultant%20SDs%20last%20for%20more%20than%202%20hours%20%28Figure%202%20b%20and%20c%29%2C%20suggesting%20a%20substantial%20mass%20supply%20by%20the%20coronal%20condensation.%20In%20the%20dip%20region%2C%20the%20total%20mass%20of%20condensation%20%281.3%20%5Cbegin%7Bequation%7D%20%5Ctimes%2010%5E%7B14%7D%20%5Cend%7Bequation%7D%20g%29%20and%20condensation%20rate%20%20%281.5%20%5Cbegin%7Bequation%7D%20%5Ctimes%2010%5E%7B10%7D%20%20%5Cend%7Bequation%7D%20g%20%20%5Cbegin%7Bequation%7D%20s%5E%7B-1%7D%20%5Cend%7Bequation%7D%29%20were%20found%20to%20be%20large%20enough%20to%20sustain%20this%20long-lived%20SD%20event%2C%20which%20has%20a%20mass%20transport%20rate%20of%207.1-12.2%20%5Cbegin%7Bequation%7D%2010%5E9%20%5Cend%7Bequation%7D%20g%20%5Cbegin%7Bequation%7D%20s%5E%7B-1%7D%20%5Cend%7Bequation%7D.%20As%20downflows%20fall%20into%20the%20sunspot%2C%20they%20eventually%20impart%20their%20energy%20into%20the%20lower%20atmosphere%20of%20sunspots%20and%20result%20in%20a%20long-lived%20localized%20brightening%20in%20the%20umbra.%20This%20SD-induced%20chromospheric%20brightening%20was%20clearly%20imaged%20by%20a%20ground-based%20solar%20telescope%2C%20the%20New%20Vacuum%20Solar%20Telescope%20%28NVST%29%2C%20located%20in%20the%20Fuxian%20Solar%20Observatory%20of%20the%20Yunnan%20Astronomical%20Observatories%20of%20the%20Chinese%20Academy%20of%20Sciences.%20This%20indicates%20that%20SDs%20play%20an%20important%20role%20in%20the%20chromosphere-corona%20mass%20cycle%20of%20the%20sunspot%20atmosphere.%0A%0A%0AFor%20the%20full%20paper%2C%20please%20check%20out%20Chen%20et%20al.%20%282022%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...859..158S/abstract\">Samanta, T., Tian, H., and Prasad Choudhary, D., ApJ 859, 158 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014ApJ...786..137T/abstract\">Tian, H., DeLuca, E., Reeves, K. K., et al., ApJ 786, 137 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015A%26A...582A.116S/abstract\">Straus, T., Fleck, B., and Andretta, V., A&A 582, A116 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016A%26A...587A..20C/abstract\">Chitta, L. P., Peter, H., and Young, P. R., A&A 587, A20 (2016)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022A%26A...659A.107C/abstract\">Chen, H., Tian, H., Li, L., et al., A&A 659, A107 (2022)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...864L...4L/abstract\">Li, L., Zhang, J., Peter, H., et al., ApJL 864, L4 (2018)</a>","","","",""],"pubDate":"2022-04-11T20:54:55.238Z"},{"id":"pod_polito_vanessa_2022-02-24T21:30:07.698Z","submitter":"Ryan French (ryan.french.14@ucl.ac.uk)","author":"Ryan J. French [1], Sarah A. Matthews [1], I. Jonathan Rae [2], Andrew W. Smith [1]","status":"published","creation-date":"2022-02-24T21:30:07.729Z","last-modified-date":"2022-03-10T22:56:44.658Z","credit":"[1] UCL Mullard Space Science Laboratory. [2] Northumbria University.","title":"Probing Current Sheet Instabilities from Flare Ribbon Dynamics","contentBlocks":[{"type":"text","text":"Current%20sheet%20instabilities%2C%20such%20as%20the%20tearing%20mode%20instability%20%28Biskamp%201986%29%2C%20are%20needed%20to%20account%20for%20the%20observed%20rate%20of%20energy%20release%20in%20solar%20flares.%20Insights%20into%20current%20sheet%20dynamics%20can%20be%20revealed%20by%20the%20behavior%20of%20flare%20ribbon%20substructure%2C%20as%20magnetic%20reconnection%20accelerates%20particles%20down%20newly%20reconnected%20field%20lines%20into%20the%20chromosphere%20to%20mark%20the%20flare%20footpoints.%20In%20this%20study%2C%20we%20use%20high-cadence%20IRIS%20Slit%20Jaw%20Imager%20%28SJI%29%20observations%20to%20probe%20for%20growth%20and%20evolution%20of%20key%20spatial%20scales%20along%20flare%20ribbons%E2%80%94resulting%20from%20dynamics%20across%20the%20current%20sheet%20of%20a%20B-class%20flare%20on%202016%20December%206.%20Combining%20analyses%20of%20spatial%20scale%20growth%20with%20Si%20IV%20nonthermal%20velocities%2C%20we%20piece%20together%20a%20timeline%20of%20flare%20onset%20for%20this%20confined%20event%2C%20and%20provide%20evidence%20of%20the%20tearing%20mode%20instability%20triggering%20a%20cascade%20and%20inverse%20cascade%20toward%20a%20power%20spectrum%20consistent%20with%20plasma%20turbulence."},{"type":"image","file":"","url":"nuggetvideos/2022/02/24/pod_polito_vanessa_2022-02-24T21%3A30%3A07.698Z/IRIS_nugget_fig1.jpg","hash":"58cb6a9682c4b4839d1797c21de10834","mimeType":"image/jpeg","caption":"Figure%201%20%E2%80%93%20Evolution%20of%20IRIS%20SJI%201400%20%26Aring%3B."},{"type":"text","text":"IRIS%20observed%20the%20flare%20with%20a%20large%20sit-and-stare%20SJI%201400%20%26Aring%3B%20window%20and%201.7%20s%20cadence.%20Figure%201%20presents%20snapshots%20of%20the%20SJI%20evolution.%20Examining%20the%20light%20curve%20and%20HMI%20LOS%20magnetic%20flux%20of%20each%20region%2C%20we%20see%20the%20two%20ribbons%20brighten%20cotemporally%2C%20tracing%20equal%20magnetic%20flux%20throughout%20their%20evolution.%20We%20therefore%20imagine%20a%20single%20flux%20tube%20passing%20from%20one%20ribbon%20to%20the%20other%2C%20containing%20the%20reconnection%20regions%20within%20it.%20%20Jeffrey%20et%20al.%20%282018%29%20examine%20the%20spectral%20evolution%20of%20the%20east%20ribbon%2C%20finding%20a%20steep%20rise%20in%20Si%20IV%201402.77%20%26Aring%3B%20nonthermal%20velocity%20%28a%20signature%20of%20plasma%20turbulence%29%20preceding%20the%20rise%20in%20Si%20IV%20intensity%20%28flare%20onset%29.%20The%20slit%20position%20can%20be%20seen%20as%20a%20bright%20vertical%20streak%20in%20Figure%201.%0A%0AWe%20track%20a%20centroid%20along%20each%20ribbon%2C%20measuring%20intensity%20variation%20as%20they%20evolve.%20Intensity%20along%20the%20ribbons%20are%20measured%20for%20every%20time%20step%2C%20producing%20the%20intensity%20stack%20plots%20in%20Figure%202%20%28left%29.%20We%20calculate%20the%20FFT%20for%20each%20cross-section%2C%20calculating%20the%20power%20of%20different%20spatial%20scales%20along%20the%20flare%20ribbons.%20We%20combine%20each%20spatial%20FFT%20into%20a%20single%20stack%20plot%2C%20also%20in%20Figure%202%20%28right%29."},{"type":"image","file":"","url":"nuggetvideos/2022/02/24/pod_polito_vanessa_2022-02-24T21%3A30%3A07.698Z/IRIS_nugget_fig2.jpg","hash":"985c6120622e411e90f1c795d9fff4f2","mimeType":"image/jpeg","caption":"Figure%202%20%E2%80%93%20Left%3A%20ribbon%20intensity%20stack%20plot.%20Right%3A%20spatial%20scale%20power%20stack%20plot%2C%20normalized%20at%20each%20spatial%20scale.%20These%20plots%20are%20for%20the%20east%20ribbon%20%28see%20paper%20for%20west%20ribbon%29."},{"type":"text","text":"In%20MHD%2C%20exponential%20growth%20at%20multiple%20spatial%20scales%20is%20a%20classical%20signal%20of%20plasma%20instability%20%28Priest%201985%29.%20We%20investigate%20growth%20at%20each%20spatial%20scale%20by%20taking%20horizontal%20cross-sections%20through%20the%20power%20spectrum%20in%20Figure%202.%20We%20determine%20the%20region%20of%20exponential%20growth%20at%20each%20scale%2C%20and%20fit%20an%20exponential%20curve%20to%20provide%20a%20growth%20rate%20and%20start%2Fend%20times%20of%20the%20exponential%20phase.%20%0A%20%0AWe%20plot%20the%20duration%20of%20exponential%20growth%20in%20Figure%203%20%28left%29.%20%20We%20see%20exponential%20growth%20start%20initially%20at%20a%20single%20spatial%20scale%2C%20before%20beginning%20at%20all%20other%20scales%20up%20to%2019%20s%20later.%20This%20is%20suggestive%20of%20a%20process%20at%20a%20specific%20spatial%20scale%20causing%20the%20growth%20at%20progressively%20shorter%20and%20longer%20scales%20through%20a%20cascade%20and%20inverse%20cascade.%20Detecting%20matching%20%28when%20scaled%29%20spatial%20scales%20in%20each%20ribbon%20provides%20confidence%20that%20processes%20are%20linked%20%E2%80%94%20both%20likely%20originating%20from%20instability%20processes%20at%20the%20reconnection%20site.%20Our%20observational%20constraints%20to%20compare%20with%20theory%20are%3A%0A1.%20%20E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href=\"https://ui.adsabs.harvard.edu/abs/2021ApJ...922..117F/abstract\">French, R. J., ApJ 922, 117 (2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1986PhFl...29.1520B/abstract\">Biskamp, D., PhFl 29, 1520 (1986)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018SciA....4.2794J/abstract\">Jefferey, N. L. S., SciA 4, 2794 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1985RPPh...48..955P/abstract\">Priest, E. R., RPPh 48, 955 (1985)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020MNRAS.491.4267T/abstract\">Tenerani A. and Velli M., MNRAS 491, 4267 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018PhRvL.121p5101D/abstract\">Dong, C., PhRvL 121, 165101 (2018)</a>","","","",""],"pubDate":"2022-03-11T19:51:21.82Z"},{"id":"pod_polito_vanessa_2022-01-21T19:08:55.089Z","submitter":"Vishal Upendran","author":"Vishal Upendran [1] and Durgesh Tripathi [1]","status":"published","creation-date":"2022-01-21T19:08:55.092Z","last-modified-date":"2022-02-09T21:11:43.161Z","credit":"[1] Inter-University Centre for Astronomy and Astrophysics, Pune, India","title":"On the formation of solar wind & switchbacks, and quiet Sun heating","contentBlocks":[{"type":"text","text":"The%20highly%20stratified%20and%20dynamic%20solar%20atmosphere%2C%20with%20temperatures%20ranging%20from%20%E2%89%885500%20K%20to%20more%20than%20a%20million%20degrees%20Kelvin%2C%20is%20tightly%20coupled%20by%20the%20dynamics%20of%20the%20magnetic%20field.%20Coronal%20Holes%20%28CH%29%20are%20morphological%20features%20seen%20as%20a%20deficit%20in%20intensity%20over%20the%20background%20Quiet%20Sun%20%28QS%29%20in%20the%20corona.%20However%2C%20at%20lower%20temperatures%2C%20i.e.%2C%20in%20the%20transition%20region%20%28TR%29%20%20and%20in%20the%20chromosphere%2C%20the%20stark%20differentiation%20between%20the%20two%20regions%20vanishes%21%20An%20example%20is%20shown%20in%20Fig.%201%2C%20with%20the%20coronal%20image%20from%20193%20%26Aring%3B%20passband%20of%20Atmospheric%20Imaging%20Assembly%20%28AIA%3B%20Boerner%20et%20al.%202012%29%20and%20the%20TR%20%28chromosphere%29%20intensity%20maps%20obtained%20in%20Si%20IV%20%28C%20II%2C%20Mg%20II%20k3%29%20from%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%3B%20De%20Pontieu%20et%20al.%202014%29.%20While%20the%20QS%20shows%20a%20larger%20radiative%20loss%20in%20the%20corona%2C%20the%20CHs%20are%20well-known%20sources%20of%20the%20solar%20wind%20%28Tu%20et%20al.%2C%202005%29.%20Hence%2C%20with%20the%20advent%20of%20high-quality%20observations%2C%20we%20demonstrate%20that%20these%20phenomena%20-%20i.e.%2C%20the%20solar%20wind%20formation%20and%20excess%20radiative%20losses%20in%20QS%20-%20may%20be%20unified%20under%20a%20single%20underlying%20scenario%20by%20studying%20the%20differences%20and%20similarities%20between%20CHs%20and%20QS."},{"type":"image","file":"","url":"nuggetvideos/2022/01/21/pod_polito_vanessa_2022-01-21T19%3A08%3A55.089Z/singleplot_FOV.png","hash":"f4f38a9db0c49fd6776c57229ebdd864","mimeType":"image/png","caption":"Fig.%201%3A%20CHs%20%28dark%29%20and%20QS%20%28bright%29%20in%20the%20corona%20%28AIA%20193%20%26Aring%3B%29%2C%20TR%20%28Si%20IV%29%20and%20the%20chromosphere%20%28C%20II%2C%20Mg%20II%20k3%29%20with%20the%20regions%20demarcated%20by%20contours%20obtained%20by%20employing%20the%20segmentation%20scheme%20of%20Upendran%20et.%20al%202020."},{"type":"text","text":"While%20prior%20studies%20report%20no%20significant%20differentiation%20between%20CHs%20and%20QS%20in%20the%20TR%20and%20chromosphere%20%28Stucki%20et%20al.%201999%29%2C%20differences%20are%20observed%20if%20the%20underlying%20photospheric%20magnetic%20flux%20density%20%28%7CB%7C%29%20is%20considered%20%28Tripathi%20et%20al.%202021%29.%20In%20these%20two%20studies%20%28Upendran%20%26amp%3B%20Tripathi%202021a%2C%202021b%29%2C%20we%20consider%205%20IRIS%20rasters%20and%20the%20corresponding%20%7CB%7C%20from%20Helioseismic%20and%20Magnetic%20Imager%20%28HMI%3B%20Scherrer%20et%20al.%202012%29%20and%20study%20the%20properties%20of%20Si%20IV%201393%20%26Aring%3B%2C%20C%20II%201334%20%26Aring%3B%2C%20and%20Mg%20II%20h%20%26amp%3B%20k%20lines%20in%20CHs%20and%20QS%20as%20a%20function%20of%20the%20%7CB%7C.%0A%0AWe%20find%20that%3A%0A1.%20Intensities%20increase%20with%20%7CB%7C%20for%20both%20regions.%20For%20similar%20%7CB%7C%2C%20QS%20shows%20excess%20intensity%20in%20both%20chromosphere%20and%20TR%20%28Fig.%202a%29%2C%20with%20larger%20excess%20in%20TR.%0A2.%20TR%20and%20chromosphere%20are%20redshifted%20on%20an%20average%2C%20with%20the%20average%20velocity%20increasing%20with%20%7CB%7C%20%28Fig.%202b%29.%0A3.%20For%20similar%20%7CB%7C%2C%20average%20velocity%20is%20consistent%20between%20regions%20in%20the%20chromosphere%2C%20while%20QS%20shows%20larger%20redshifts%20in%20TR%20%28Fig.%202b%29."},{"type":"image","file":"","url":"nuggetvideos/2022/01/21/pod_polito_vanessa_2022-01-21T19%3A08%3A55.089Z/Comb.png","hash":"6b34dbeb004e4fc7c06835b58ef0eb03","mimeType":"image/png","caption":"Fig.%202%3A%20QS-CH%20differences%20as%20a%20function%20of%20%7CB%7C%20in%20the%20TR%20and%20chromosphere.%20The%20intensity%20ratio%20is%20depicted%20in%20panel%20a%20and%20velocity%20differences%20in%20other%20panels.%20Panel%20b%20depicts%20the%20difference%20in%20average%20velocity%2C%20while%20panels%20c%20%26amp%3B%20d%20show%20for%20the%20blue-%20and%20red%20shifted%20pixels%20alone.%20The%20quantities%20are%20binned%20in%20%7CB%7C%20to%20improve%20statistics%2C%20and%20the%20error%20bars%20are%20standard%20error%20over%20the%20mean."},{"type":"text","text":"Next%2C%20we%20separately%20consider%20the%20blue-shifted%20and%20red-shifted%20pixels%20to%20study%20the%20systematic%20effects%20of%20%7CB%7C%20on%20the%20signed%20velocities.%20We%20find%20the%20blue%20and%20redshifts%20to%20increase%20with%20%7CB%7C%2C%20with%20the%20CHs%20showing%20excess%20blueshifts%20in%20both%20the%20chromosphere%20and%20the%20TR%20%28see%20Fig.%202c%29.%20However%2C%20the%20QS%20shows%20excess%20redshifts%20in%20TR%2C%20while%20CHs%20show%20excess%20redshifts%20in%20the%20chromosphere%2C%20presenting%20a%20dichotomy%20between%20the%20chromosphere%20and%20TR%20%28see%20Fig.%202d%29.%0A%0ATo%20understand%20further%2C%20we%20investigate%20the%20cross-correlation%20between%20TR%20and%20chromospheric%20velocities.%20We%20find%3A%0A1.%20TR%20and%20chromospheric%20up-%20and%20downflows%20are%20well%20correlated%20%28Fig.%203a%26amp%3Bb%29.%0A2.%20TR%20upflows%20are%20also%20well%20correlated%20with%20chromospheric%20downflows%20%28Fig.%203c%29%2C%20while%20no%20correlations%20are%20seen%20vice-versa%20%28Fig.%203d%29.%0A3.%20QS%20shows%20excess%20deceleration%20of%20downflows.%0A4.%20CHs%20show%20excess%20acceleration%20of%20upflows."},{"type":"image","file":"","url":"nuggetvideos/2022/01/21/pod_polito_vanessa_2022-01-21T19%3A08%3A55.089Z/singleplot_SiMgk3correlation.png","hash":"8604a572c80d88ca30aa106f1ca76ff9","mimeType":"image/png","caption":"Fig.%203%3A%20TR%20and%20chromospheric%20flow%20correlations%2C%20with%20the%20TR%20flows%20depicted%20in%20bins%20of%20chromospheric%20flows.%20Note%20that%20up-flows%20are%20blueshifts%2C%20and%20downflows%20are%20redshifts"},{"type":"text","text":"These%20observations%20may%20be%20explained%20by%20impulsive%20heating%20in%20a%20stratified%20atmosphere%20and%20different%20magnetic%20field%20topologies%20in%20CHs%20and%20QS.%20In%20the%20CHs%20%28Fig.%204a%29%2C%20the%20lesser%20%28similar%29%20number%20of%20long%20%28short%29%20loops%20give%20rise%20to%20a%20deficit%20in%20intensity%20%28similar%20gross%20intensity%29%20when%20compared%20to%20QS%20in%20the%20corona%20%28TR%20and%20chromosphere%29.%20The%20excess%20open%20flux%20undergoes%20interchange%20reconnection%20with%20adjoining%20closed%20loops%20of%20different%20heights%2C%20leading%20to%20bidirectional%20flows.%20The%20upflows%20are%20preferentially%20accelerated%20along%20the%20open%20field%20under%20the%20assumption%20of%20mass%20flux%20conserving%20flows%20%26amp%3B%20reduced%20coronal%20pressure%20in%20CHs%20and%20are%20seen%20as%20excess%20CH%20upflows%2C%20while%20the%20downflows%20radiatively%20cool%20to%20be%20visible%20in%20cooler%20lines.%20The%20correlated%20downflows%20may%20be%20explained%20if%20a%20fraction%20of%20the%20up-flowing%20plasma%20may%20cool%20down%20and%20fall%20back%2C%20or%20reconnection%20events%20much%20higher%20in%20the%20atmosphere%20drive%20such%20flows.%20An%20interesting%20consequence%20of%20interchange%20reconnection%20is%20the%20potential%20for%20these%20kinked%20field%20lines%20to%20propagate%20outwards%20as%20switchbacks%20%28Zank%20et%20al.%202020%29%20-%20in%20such%20a%20scenario%2C%20the%20flows%20we%20obtain%20serve%20as%20strong%20constraints%20on%20the%20possibility%20of%20low%20atmosphere%20switchback%20formation."},{"type":"image","file":"","url":"nuggetvideos/2022/01/21/pod_polito_vanessa_2022-01-21T19%3A08%3A55.089Z/Topology.png","hash":"4362d3b1d45da9d266238ff76fc50ef1","mimeType":"image/png","caption":"Fig.4%3A%20A%20schematic%20depicting%20the%20proposed%20picture%20of%20impulsive%20heating%20occurring%20across%20different%20magnetic%20field%20topologies.%20In%20the%20left%20panel%2C%20we%20show%20a%20CH%20topology%2C%20including%20open%20funnel-like%20structure%20%28black%29%2C%20closed%20loops%20of%20varying%20sizes%20%28yellow%29%2C%20and%20impulsive%20events%20%28red%20asterisks%29%20due%20to%20interchange%20reconnection%20between%20the%20open%20and%20closed%20field%20lines%2C%20giving%20rise%20to%20bidirectional%20flows%20%28blue%20and%20red%20arrows%29.%20The%20kinked%20field%20line%20propagating%20outward%20as%20a%20switchback%20is%20depicted%20as%20a%20dashed%20line%2C%20with%20the%20approximate%20propagation%20direction%20by%20black%20arrows.%20Right%20panel%3A%20QS%20topology%20shown%20with%20the%20same%20terminology%20as%20left%20panel."},{"type":"text","text":"Finally%2C%20the%20QS%20contains%20closed-loop%20structures%20predominantly%20%28see%20Fig.%204b%29%2C%20and%20closed-loop%20reconnection%20very%20much%20gives%20rise%20to%20the%20various%20correlated%20flows.%20However%2C%20due%20to%20confined%20plasma%20within%20loops%2C%20downflows%20are%20preferentially%20decelerated%20more%20in%20QS%20over%20CHs%2C%20while%20the%20upflows%20are%20not%20accelerated%20in%20this%20topology.%20Thus%2C%20a%20unified%20reconnection%20mechanism%20in%20different%20magnetic%20field%20topological%20settings%20elegantly%20gives%20rise%20to%20coronal%20heating%2C%20solar%20wind%20origin%2C%20and%20switchback%20formation."}],"references":["<a 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Zank et al 2020 ApJ 903 1</a>"],"pubDate":"2022-02-09T21:12:07.272Z"},{"id":"pod_polito_vanessa_2021-12-13T18:32:29.569Z","submitter":"Paola Testa (SAO)","author":"Paola Testa [1], Vanessa Polito [2], Bart De Pontieu [3,4,5]","status":"published","creation-date":"2021-12-13T18:32:29.572Z","last-modified-date":"2022-01-07T18:16:30.292Z","credit":"[1] Harvard-Smithsonian Center for Astrophysics; [2] Bay Area Environmental Research Institute; [3] Lockheed Martin Solar & Astrophysics Laboratory; [4] Rosseland Center for Solar Physics, Univ. of Oslo; [5] Institute of Theoretical Astrophysics, Univ. of Oslo","title":"Insights into the heating of the hot non-flaring corona: IRIS observations of nanoflares and loop modeling","contentBlocks":[{"type":"text","text":"The%20heating%20of%20the%20solar%20corona%20is%20one%20of%20the%20main%20open%20issues%20in%20astrophysics.%20The%20heating%20mechanisms%20likely%20operate%20on%20small%20spatial%20and%20temporal%20scales%2C%20and%20it%20is%20quite%20challenging%20to%20detect%20single%20coronal%20heating%20events%2C%20especially%20in%20the%20corona%20where%20efficient%20thermal%20conduction%20smears%20the%20heating%20signatures.%0AThe%20core%20of%20solar%20Active%20Regions%20%28ARs%29%20is%20where%20the%20hottest%20%28%5Cbegin%7Bequation%7D%20%5Cgtrsim%20%5Cend%7Bequation%7D5MK%29%20coronal%20plasma%20is%20observed%20outside%20flares.%20This%20hot%20emission%20is%20typically%20transient%2C%20and%20the%20signatures%20of%20single%20heating%20events%20can%20sometimes%20be%20detected%20as%20short-lived%20brightenings%20of%20the%20footpoint%20emission%2C%20as%20shown%20in%20two%20examples%20in%20Figure%201.%20The%20unprecedented%20high%20spatial%20and%20temporal%20resolution%20of%20IRIS%20is%20crucial%20to%20observe%20this%20highly%20variable%20emission."},{"type":"image","file":"","url":"nuggetvideos/2021/12/13/pod_polito_vanessa_2021-12-13T18%3A32%3A29.569Z/iris_nugget_fig1.png","hash":"db0ac610af7e4c5892921bb252ec982","mimeType":"image/png","caption":"Figure%201%3A%20IRIS%201400%20%26Aring%3B%20slit-jaw%20images%20%28left%29%20and%20AIA%2094%20%26Aring%3B%20images%20%28right%29%20for%20two%20events%20showing%20rapid%20moss%20brightenings%20at%20the%20loop%20footpoints%20%28observed%20in%20the%20Si%20IV%20%E2%88%BC1400%20%26Aring%3B%20transition%20region%20emission%29%20followed%20%28note%20the%20different%20times%20of%20the%20two%20images%29%20by%20transient%20brightenings%20of%20the%20overlying%20hot%20%28%7E5%E2%80%938%20MK%29%20loops%20%28observed%20in%20the%20AIA%2094%20%26Aring%3B%2C%20which%20is%20here%20dominated%20by%20FeXVIII%20emission%29.%20%28Figure%20adapted%20from%20Fig.1%20of%20Testa%2C%20Polito%20%26amp%3B%20De%20Pontieu%202020%29"},{"type":"text","text":"IRIS%20spectral%20observations%20of%20the%20response%20of%20the%20lower%20atmosphere%20%28transition%20region%20and%20chromosphere%29%20to%20coronal%20heating%20events%20provides%20%28Testa%20et%20al.%202014%2C%202020%3B%20Polito%20et%20al.%202018%29%20tight%20constraints%20on%20the%20properties%20of%20the%20heating%20events%20%28e.g.%2C%20duration%2C%20total%20energy%29%20and%20on%20the%20mechanisms%20of%20energy%20transport%20%28e.g.%2C%20non-thermal%20particles%20accelerated%20during%20magnetic%20reconnection%20events%2C%20thermal%20conduction%29.%20Early%20analysis%20of%20IRIS%20observations%20of%20this%20type%20of%20events%20showed%20the%20diagnostic%20potential%20of%20the%20Doppler%20shift%20of%20the%20Si%20IV%20emission%2C%20in%20particular%20with%20sometimes%20observed%20blueshift%20providing%20a%20strong%20indication%20of%20the%20presence%20of%20non-thermal%20particles%2C%20and%20even%20providing%20constraints%20on%20the%20parameters%20of%20their%20distribution%20%28Testa%20et%20al.%202014%29.%20Hard%20X-ray%20observations%20of%20non-thermal%20particles%20indicate%20that%20their%20emission%20is%20generally%20compatible%20with%20power-law%20distribution.%20One%20of%20the%20main%20parameters%20of%20these%20power-laws%20is%20the%20low-energy%20cutoff%20%28%5Cbegin%7Bequation%7D%20E_C%20%5Cend%7Bequation%7D%29%20which%20is%20crucial%20to%20determine%20the%20total%20energy%20in%20the%20accelerated%20electrons.%20%5Cbegin%7Bequation%7D%20E_C%20%5Cend%7Bequation%7D%20%20is%20often%20difficult%20to%20determine%20from%20hard%20X-ray%20observations%20because%20%20of%20the%20overall%20of%20thermal%20and%20non-thermal%20spectra.%20The%20IRIS%20emission%20observed%20at%20the%20footpoint%20of%20AR%20hot%20loops%20heated%20by%20nanoflares%20are%20highly%20sensitive%20to%20the%20energy%20of%20the%20non-thermal%20electrons%2C%20providing%20excellent%20diagnostics%20of%20%5Cbegin%7Bequation%7D%20E_C%20%5Cend%7Bequation%7D%29%20for%20very%20small%20heating%20events%20typically%20below%20detection%20thresholds%20of%20hard%20X-ray%20observatories.%0A%0AIn%20order%20to%20diagnose%20the%20properties%20of%20the%20heating%2C%20and%20the%20presence%20and%20properties%20of%20the%20non-thermal%20particles%2C%20modeling%20of%20the%20atmospheric%20plasma%20response%20to%20nanoflares%20is%20needed.%20The%20%20RADYN%20code%20%28Carlsson%20%26amp%3B%20Stein%201997%2C%20Allred%20et%20al.%202005%2C%202015%29%20is%20well%20suited%20to%20these%20studies%20as%20it%20includes%20non-Local%20Thermodynamic%20Equilibrium%20%28non-LTE%29%20radiative%20transfer%2C%20which%20is%20necessary%20to%20model%20the%20chromospheric%20emission%2C%20and%20it%20allows%20to%20model%20heating%20also%20by%20non-thermal%20electrons.%20In%20Testa%20et%20al.%20%282014%29%20we%20conducted%20an%20initial%20exploration%20of%20the%20parameter%20space%20of%201D%20loop%20models%2C%20which%20showed%20the%20potential%20of%20diagnostics%20of%20the%20IRIS%20Si%20IV%20spect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href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...889..124T/abstract\">Testa, Polito & De Pontieu, ApJ 889, 124 (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014Sci...346B.315T/abstract\">Testa, et al. Science, Volume 346, 315 (2014)</a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2018ApJ...856..178P/abstract"\"> Polito et al., ApJ, 856, 178 (2018)</a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/1997LNP...489..159C/abstract"\"> Carlsson & Stein LNP, 489, 159, (1997)</a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2005ApJ...630..573A/abstract"\"> Allred et al., ApJ, 630, 573 (2005)</a>","<a href=\"âÂÂÂÂÂÂÂÂÂÂhttps://ui.adsabs.harvard.edu/abs/2015ApJ...809..104A/abstract"\"> Allred et al., ApJ, 809, 104, (2015)</a>","","","",""],"pubDate":"2022-01-10T21:28:50.841Z"},{"id":"pod_polito_vanessa_2021-11-22T17:44:45.468Z","submitter":"Daniel Nobrega-Siverio (dnobrega@iac.es)","author":"Daniel Nobrega-Siverio [1,2,3,4], Salvo Guglielmino [5,6], Alberto Sainz Dalda [7,8,9]","status":"published","creation-date":"2021-11-22T17:44:45.471Z","last-modified-date":"2021-12-08T20:28:20.391Z","credit":"[1] Instituto de Astrofisica de Canarias. [2] Universidad de La Laguna. [3] Rosseland Centre for Solar Physics. [4] Institute of Theoretical Astrophysics. [5] Dipartimento di Fisica e Astronomia - Ettore Majorana. [6] INAF - Osservatorio Astrofisico di Catania. [7] Lockheed Martin Solar and Astrophysics Laboratory. [8] Bay Area Environmental Research Institute. [9] Stanford University.","title":"Solar surges related to UV bursts: Characterization through k-means, inversions, and density diagnostics.","contentBlocks":[{"type":"text","text":"Surges%20are%20key%20chromospheric%20ejections%20closely%20related%20to%20other%20solar%20phenomena%20such%20as%20UV%20bursts%20and%20coronal%20jets.%20Even%20though%20surges%20have%20been%20observed%20for%20decades%20now%2C%20questions%20regarding%20their%20fundamental%20physical%20properties%20such%20as%20temperature%20and%20density%2C%20as%20well%20as%20their%20impact%20on%20upper%20layers%20of%20the%20solar%20atmosphere%20remain%20open.%20In%20this%20study%20%28Nobrega-Siverio%20et%20al.%202021%29%2C%20we%20address%20the%20current%20lack%20of%20inverted%20models%20and%20diagnostics%20of%20surges%2C%20characterizing%20the%20chromospheric%20and%20transition%20region%20plasma%20of%20these%20phenomena.%20To%20that%20end%2C%20we%20have%20analyzed%20an%20episode%20of%20recurrent%20surges%20related%20to%20UV%20bursts%20observed%20in%20April%202016%20with%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%2C%20focusing%20on%20the%20near-%20and%20far-UV%20spectra%20obtained%20through%20dense%2064-step%20raster%20scans%20%28see%20also%20Guglielmino%20et%20al.%202019%29.%0A%0ALeft%20column%20of%20Figure%201%20shows%20radiance%20maps%20of%20Mg%20II%20k%202796.3%20%26Aring%3B%20for%20the%20four%20rasters%20studied%2C%20where%20the%20surges%20are%20clearly%20distinguishable%20as%20dark%20structures%20delimited%20by%20a%20solid%20contour.%20To%20analyze%20the%20Mg%20II%20h%26amp%3Bk%20spectra%2C%20we%20have%20used%20k-means%3A%20a%20machine%20learning%20technique%20that%20can%20be%20used%20to%20classify%20a%20set%20of%20profiles%20in%20k%20disjoint%20clusters%20%28or%20groups%29%20based%20on%20the%20similarity%20of%20the%20profiles%20%28see%20the%20Scikit-learn%20Python%20tools%20by%20Pedregosa%20et%20al.%202011%29.%20By%20doing%20this%2C%20we%20can%20obtain%20Mg%20II%20h%26amp%3Bk%20representative%20profiles%20from%20the%20observations%2C%20also%20reducing%20the%20number%20of%20profiles%20to%20invert.%20The%20second%20column%20of%20Figure%201%20contains%20the%20distribution%20of%20the%20160%20clusters%20per%20raster%20obtained%20with%20the%20k-means.%20By%20ordering%20the%20clusters%20depending%20on%20their%20number%20of%20profiles%2C%20we%20can%20already%20discern%20that%20surges%20and%20their%20surroundings%20have%20clearly%20different%20Mg%20II%20h%26amp%3Bk%20profiles%20from%20other%20regions."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_02 (3).png","hash":"83df248a9a1c4377edcb4180978d5046","mimeType":"image/png","caption":"Figure%201.%20Observed%20surges%20and%20results%20from%20k-means%20and%20inversions.%20Columns%20from%20left%20to%20right%3A%20radiance%20maps%20in%20the%20core%20of%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20line%3B%20cluster%20labels%20from%20the%20k-means%20ordered%20by%20the%20amount%20of%20profiles%20within%20a%20cluster%3B%20and%20maps%20at%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-5.2%20for%20temperature%2C%20T%2C%20electron%20number%20density%2C%20%5Cbegin%7Bequation%7Dn_e%2C%5Cend%7Bequation%7D%20and%20line-of-sight%20velocity%2C%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%2C%20from%20the%20inversions%20of%20the%20Mg%20II%20h%26amp%3Bk%20line%20using%20the%20STiC%20code.%20Black%20contours%20delimit%20the%20bulk%20of%20the%20surges%20visible%20in%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20radiance%20maps."},{"type":"text","text":"Once%20we%20obtain%20the%20representative%20Mg%20II%20h%26amp%3Bk%20profiles%20from%20the%20k-means%2C%20we%20invert%20them%20using%20the%20state-of-the-art%20STiC%20code%20%28de%20la%20Cruz%20Rodriguez%20et%20al.%202019%29.%20The%20three%20rightmost%20columns%20of%20Figure%201%20show%20the%20results%20from%20the%20inversions%20for%20temperature%2C%20electron%20number%20density%20and%20line-of-sight%20velocity%20at%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%3D-5.2.%20In%20the%20maps%2C%20it%20is%20possible%20to%20perceive%20that%20the%20surges%20have%20some%20peculiarities%20in%20their%20physical%20properties%2C%20for%20example%2C%20they%20are%20mostly%20cooler%20and%20with%20a%20smaller%20electron%20number%20density%20%20than%20their%20surroundings.%20To%20get%20a%20whole%20perspective%20of%20these%20properties%2C%20we%20have%20performed%20a%20statistical%20analysis%20within%20the%20contour%20that%20delimits%20the%20different%20surges%20in%20Figure%201.%20The%20results%20are%20shown%20in%20Figure%202%2C%20through%20histograms%20for%20the%20three%20above-mentioned%20physical%20quantities.%20To%20create%20these%20histograms%2C%20we%20considered%20the%20range%20of%20optical%20depths%20in%20which%20the%20uncertainties%20are%20smaller%20for%20each%20physical%20quantity."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_04 (2).png","hash":"45a020217fce224a83b3590e3ac3a213","mimeType":"image/png","caption":"Figure%202.%20Statistical%20results%20for%20T%2C%20%5Cbegin%7Bequation%7Dn_e%5Cend%7Bequation%7D%2C%20and%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20obtained%20within%20the%20contour%20that%20delimits%20the%20different%20surges%20in%20Figure%201.%20The%20statistics%20contain%20data%20from%20the%20optical%20depths%20where%20inversions%20are%20more%20reliable%2C%20from%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-6.0%20to%20-3.2%2C%20for%20the%20temperature%2C%20and%20from%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-6.0%20to%20-4.8%20for%20the%20density%20and%20velocity.%20Histograms%20are%20stacked%20by%20rasters%2C%20showing%20that%20the%20different%20surges%20have%20similar%20properties%2C%20and%20by%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%2C%20illustrating%20the%20variation%20of%20the%20physical%20parameters%20with%20the%20optical%20depth."},{"type":"text","text":"From%20the%20histograms%2C%20we%20conclude%20that%20the%20surges%20have%20their%20most%20probable%20temperature%20around%206000%20K%2C%20electronic%20number%20densities%20mostly%20concentrated%20from%20%5Cbegin%7Bequation%7D1.6%5Ctimes10%5E%7B11%7D%5Cend%7Bequation%7D%20to%20%5Cbegin%7Bequation%7D10%5E%7B12%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%2C%20and%20velocities%20of%20a%20few%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B-1%7D%5Cend%7Bequation%7D.%20In%20addition%2C%20we%20have%20shown%20that%20the%20statistical%20distributions%20of%20these%20properties%20are%20very%20similar%20for%20the%20different%20surges%2C%20meaning%20that%20these%20ejections%20can%20be%20well%20constrained%20in%20terms%20of%20their%20physical%20quantities.%0A%0A%0AWe%20have%20also%20studied%20the%20transition%20region%20of%20surges%20through%20the%20far-UV%20spectra%2C%20being%20able%20to%20find%20for%20the%20first%20time%20detectable%20emission%20in%20both%20the%20O%20IV%201399.8%20%26Aring%3B%20and%201401.2%20%26Aring%3B%20lines%20related%20to%20surges.%20This%20finding%20is%20relevant%20because%20it%20clearly%20demonstrates%20that%20surges%20have%20a%20transition%20region%20counterpart%20even%20in%20the%20weakest%20far-UV%20lines%2C%20as%20well%20as%20it%20gives%20observational%20support%20to%20the%20theoretical%20predictions%20by%20Nobrega-Siverio%20et%20al.%202018.%20Figure%203%20contains%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20radiance%20map%20together%20with%20O%20IV%20radiance%20maps%20at%20different%20positions%2C%20showing%20that%20the%20location%20of%20the%20brightest%20O%20IV%20regions%20can%20be%20found%20within%20the%20bulk%20of%20the%20surges%20and%2For%20in%20their%20boundaries%20following%20the%20threads%20of%20the%20surges.%20This%20is%20particularly%20evident%20in%20the%20third%20and%20fourth%20rasters."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_05.png","hash":"2f17503f528a55da88dab6b628b966f1","mimeType":"image/png","caption":"Figure%203.%20Radiance%20maps%20showing%20the%20O%20IV%20emissivity%20of%20the%20surges.%20From%20left%20to%20right%3A%20Radiance%20maps%20in%20the%20core%20of%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20line%20%28first%20column%29%3B%20in%20the%20core%20of%20the%20O%20IV%201401.2%20%26Aring%3B%20line%20%28second%20column%29%3B%20in%20the%20blue%20and%20red%20wings%20at%20-50%20and%200%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B-1%7D%5Cend%7Bequation%7D%20of%20O%20IV%201401.2%20%26Aring%3B%20%28third%20and%20fourth%20columns%2C%20respectively%29%3B%20and%20composite%20image%20of%20the%20blue%20and%20red%20wing%20radiance%20maps%20%28fifth%20column%29.%20Equivalent%20maps%20are%20plotted%20for%20the%20O%20IV%201399.8%20%26Aring%3B%20line%20%28sixth%20to%20ninth%20columns%29.%20The%20contours%20are%20the%20same%20as%20in%20Figure%201."},{"type":"text","text":"The%20simultaneous%20finding%20of%20O%20IV%201399.8%20%26Aring%3B%20and%201401.2%20%26Aring%3B%20allowed%20us%20to%20estimate%20the%20electron%20density%20in%20the%20transition%20region%20of%20the%20surges.%20Applying%20density%20diagnostics%20%28see%2C%20e.g.%2C%20Polito%20et%20al.%202016%29%2C%20we%20obtained%20a%20electron%20number%20density%20in%20the%20range%20of%20%5Cbegin%7Bequation%7D2.5%5Ctimes10%5E%7B10%7D%20-10%5E%7B12%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%20for%20the%20surge%20layers%20emitting%20in%20the%20far-UV.%0A%0AIn%20this%20work%2C%20we%20have%20also%20qualitatively%20compared%20the%20observations%20with%20three%20surge%20numerical%20experiments%20%28Nobrega-Siverio%20et%20al.%202016%2C%202017%2C%202018%29%20performed%20with%20the%20Bifrost%20code%20%28Gudiksen%20et%20al.%202011%29.%20Figure%204%20shows%20the%20electron%20number%20density%20for%20these%20three%20simulations%2C%20with%20superimposed%20contours%20at%20different%20temperatures%20that%20highlight%20the%20multi-thermal%20structure%20of%20these%20ejections.%20We%20have%20found%20similarities%20in%20terms%20of%20the%20topology%20that%20may%20also%20explain%20the%20location%20of%20the%20observed%20brightest%20O%20IV%20regions%20with%20respect%20to%20the%20bulk%20of%20the%20surges.%20In%20addition%2C%20the%20core%20of%20the%20simulated%20surges%20is%20quite%20concentrated%20around%206000%20K%2C%20which%20agrees%20with%20the%20values%20from%20the%20inversions%20we%20have%20found%20here."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_07 (1).png","hash":"4b96f8b3619623126bd457fe9f5fc75b","mimeType":"image/png","caption":"Figure%204.%20Electron%20number%20density%20for%20three%20different%20simulated%20surges.%20Contours%20of%20temperature%20are%20superimposed%20for%20T%3D6%20kK%20%28green%29%2C%20T%3D10%20kK%20%28blue%29%2C%20and%20T%3D200%20kK%20%28red%29.%20Panel%20A%3A%20Surge%20from%20Nobrega-Siverio%20et%20al.%202016.%20Panels%20B%20and%20C%3A%20Surges%20from%20Nobrega-Siverio%20et%20al.%202017%2C%202018."},{"type":"text","text":"The%20combination%20of%20methods%20and%20results%20obtained%20in%20this%20work%20opens%20new%20possibilities%20for%20the%20analysis%20and%20diagnostics%20of%20surges%2C%20and%20an%20ISSI%20team%20devoted%20to%20unravel%20the%20surges%20is%20currently%20exploring%20them%20%28see%20https%3A%2F%2Fteams.issibern.ch%2Funravelingsurges%2F%20for%20further%20details%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...655A..28N/abstract\"> Nobrega-Siverio, D., Guglielmino, S. L., & Sainz Dalda, A. 2021, A&A, 655, A28 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\"> De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Sol. Phys., 289, 2733</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...871...82G/abstract\"> Guglielmino, S. L., Young, P. R., & Zuccarello, F. 2019, ApJ, 871, 82 </a>","<a href=\"https://www.jmlr.org/papers/volume12/pedregosa11a/pedregosa11a.pdf\"> Pedregosa, F., Varoquaux, G., Gramfort, A., et al. 2011, J. Mach. Learn. Res., 12, 2825 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019A%26A...623A..74D/abstract\"> de la Cruz Rodriguez, J., Leenaarts, J., Danilovic, S., & Uitenbroek, H. 2019, A&A, 623, A74 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016A%26A...594A..64P/abstract\"> Polito, V., Del Zanna, G., Dudik, J., et al. 2016a, A&A, 594, A64 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...858....8N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., & Martinez-Sykora, J. 2018, ApJ, 858, 8 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2011A%26A...531A.154G/abstract\"> Gudiksen, B. V., Carlsson, M., Hansteen, V. H., et al. 2011, A&A, 531, A154 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...822...18N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., & Martinez-Sykora, J. 2016, ApJ, 822, 18 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...850..153N/abstract\"> Nobrega-Siverio, D., Martinez-Sykora, J., & Moreno-Insertis, F. & Rouppe van der Voort. L. 2017, ApJ, 850, 153 </a>"],"pubDate":"2021-12-09T20:35:14.976Z"},{"id":"pod_polito_vanessa_2021-10-26T21:53:23.861Z","submitter":"Milan Gosic","author":"Milan Gosic [1,2], Bart De Pontieu [1,3,4], Luis R. Bellot Rubio [5], Alberto Sainz Dalda [1,2], Sara Esteban Pozuelo [5,6,7]","status":"published","creation-date":"2021-10-26T21:53:23.864Z","last-modified-date":"2021-11-10T20:10:04.704Z","credit":"[1] Lockheed Martin Solar and Astrophysics Laboratory, [2] Bay Area Environmental Research Institute, [3] Institute of Theoretical Astrophysics at the University of Oslo [4] Rosseland Centre for Solar Physics at the University of Oslo, [5] Instituto de Astrofisica de Andalucia, [6], Instituto de Astrofisica de Canarias, [7] Departamento de Astrofisica, Universidad de La Laguna","title":"Emergence of Internetwork Magnetic Fields through the Solar Atmosphere","contentBlocks":[{"type":"text","text":"Internetwork%20%28IN%29%20magnetic%20fields%20are%20weak%2C%20short-lived%2C%20but%20highly%20dynamic%20magnetic%20structures%20that%20emerge%20all%20over%20the%20Sun.%20They%20bring%20an%20enormous%20amount%20of%20magnetic%20flux%20to%20the%20solar%20surface%20and%20maintain%20the%20quiet%20Sun%20network%20%28NW%29.%20Because%20of%20this%2C%20IN%20fields%20are%20considered%20to%20be%20an%20essential%20contributor%20to%20the%20photospheric%20flux%20and%20energy%20budget%2C%20and%20may%20have%20a%20substantial%20impact%20on%20the%20energetics%20and%20dynamics%20of%20the%20upper%20solar%20atmosphere.%0A%0AThe%20presence%20of%20polarization%20signals%20due%20to%20IN%20magnetic%20fields%20in%20the%20chromosphere%20has%20not%20%20been%20observationally%20confirmed%20yet%20due%20to%20insufficient%20sensitivity%20of%20the%20available%20measurements.%20It%20is%20unknown%20if%20these%20fields%20can%20rise%20up%20to%20the%20chromosphere%20and%20beyond.%20Also%2C%20MHD%20models%20do%20not%20consistently%20show%20IN%20magnetic%20loops%20reaching%20the%20chromosphere.%20It%20is%20therefore%20necessary%20to%20study%20the%20possible%20presence%20and%20nature%20of%20IN%20fields%20in%20the%20upper%20atmosphere.%0A%0AIn%20this%20study%20we%20use%20coordinated%2C%20high-resolution%2C%20multi-wavelength%20observations%20obtained%20with%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%20and%20the%20Swedish%201-m%20Solar%20Telescope%20%28SST%2C%20Scharmer%20et%20al.%202003%29%20to%20follow%20the%20evolution%20of%20IN%20magnetic%20loops%20emerging%20through%20the%20solar%20atmosphere.%20%0A%0AThe%20panels%20presented%20in%20Figure%201%20show%20three%20IN%20clusters%20%28the%20red%2C%20green%2C%20and%20blue%20contours%29%20emerging%20in%20the%20photosphere%20%28panels%20E%20and%20F%29%20and%20rinsing%20through%20the%20chromospheric%20layers%20%28G%29.%20%EF%BB%BFThe%20SJI%201400%20%26Aring%3B%20images%20%28H%29%20reveal%20a%20lot%20of%20bright%20loops%20connecting%20the%20footpoints%2C%20and%20also%20the%20footpoints%20with%20the%20surrounding%20NW%20patches.%20Many%20of%20these%20bright%20loops%20are%20the%20result%20of%20the%20heating%20generated%20by%20reconnection%20of%20the%20emerging%20and%20ambient%20magnetic%20field%20lines%20and%20are%20likely%20caused%20by%20Si%20IV%20emission.%20The%20C%20II%20and%20Si%20IV%20lines%20%28A%2C%20B%20and%20C%29%20indicate%20that%20the%20Doppler%20velocities%20change%20from%20blueshifts%20to%20redshifts%20when%20moving%20from%20the%20southern%20to%20the%20northern%20parts%20of%20the%20emission%20enhancement.%20This%20is%20compatible%20with%20what%20would%20be%20expected%20from%20bidirectional%20outflows%20produced%20by%20reconnection%20events%2C%20which%20lead%20to%20greatly%20broadened%20spectral%20lines."},{"type":"image","file":"","url":"nuggetvideos/2021/10/26/pod_polito_vanessa_2021-10-26T21%3A53%3A23.861Z/Fig1.png","hash":"6150e061434d99aeb879c46082642460","mimeType":"image/png","caption":"Figure%201%3A%20Upper%20row%3A%20IRIS%20rasters%20in%20the%20C%20II%201335%20%26Aring%3B%2C%20Si%20IV%201394%20%26Aring%3B%2C%20Si%20IV%201403%20%26Aring%3B%2C%20and%20Mg%20II%202796%20%26Aring%3B%20spectral%20domains.%20The%20black%2C%20red%2C%20and%20violet%20horizontal%20lines%20mark%20positions%20along%20the%20slit%20for%20which%20we%20analyzed%20in%20detail%20the%20recorded%20IRIS%20FUV%20and%20NUV%20spectra.%20Bottom%20row%3A%20SST%20continuum%20intensity%20maps%20and%20magnetograms%20in%20the%20Fe%20I%206173%20%26Aring%3B%20line%2C%20IRIS%20SJI%202796%20%26Aring%3B%20and%20SJI%201400%20%26Aring%3B%20intensity%20maps."},{"type":"text","text":"The%20chromospheric%20response%20to%20the%20emerging%20IN%20fields%20can%20be%20seen%20in%20the%20Ca%20II%20and%20H%CE%B1%20images.%20They%20show%20us%20that%20the%20chromospheric%20fibrils%20have%20completely%20changed%20their%20morphology%20during%20the%20emergence%20of%20the%20three%20IN%20clusters.%20Figure%202%20%28panels%20A%20to%20D%29%20shows%20one%20of%20the%20most%20interesting%20moments%20when%20long%20and%20wide%20blueshifted%20H%CE%B1%20absorption%20features%20appear%20above%20the%20negative-polarity%20footpoints%2C%20and%20extend%20down%20to%20the%20positive-polarity%20NW%20patch.%20They%20may%20outline%20magnetic%20field%20lines%20rising%20intermittently%20through%20the%20atmosphere%20and%20reconnecting%20with%20the%20ambient%20fields%20above.%20Simultaneously%2C%20the%20Ca%20II%20images%20%28E%20to%20G%29%20reveal%20the%20fibrils%20clearly%20rooted%20in%20the%20footpoints%20of%20the%20clusters.%20After%20the%20blueshift%20event%2C%20the%20Ca%20II%20magnetograms%20%28H%29%20start%20showing%20the%20positive-%20and%20negative-polarity%20footpoints%20created%20by%20the%20three%20clusters."},{"type":"image","file":"","url":"nuggetvideos/2021/10/26/pod_polito_vanessa_2021-10-26T21%3A53%3A23.861Z/Fig2.png","hash":"46655d4743c8f81f6629550531af6bfa","mimeType":"image/png","caption":"Figure%202%3A%20Chromospheric%20fibrils%20above%20the%20emerging%20IN%20flux%20region%20can%20be%20seen%20as%20blueshifted%20H%CE%B1%20absorption%20features%20%28panels%20A%20to%20D%29%20and%20in%20the%20Ca%20II%20filtergrams%20at%20%E2%88%920.2%20%26Aring%3B%20%28panel%20E%29%2C%20the%20line%20core%20%28F%29%2C%20and%200.2%20%26Aring%3B%20%28G%29.%20The%20panel%20%28H%29%20displays%20the%20Ca%20II%20magnetogram%20showing%20the%20negative-polarity%20IN%20footpoints%20appearing%20in%20the%20chromosphere%20%28green%20contour%29."},{"type":"text","text":"The%20scenario%20in%20which%20the%20newly%20emerging%20fields%20rise%20through%20the%20solar%20atmosphere%20and%20interact%20with%20the%20ambient%20fields%20is%20supported%20by%20the%20FUV%20IRIS%20spectra.%20Figure%203%20shows%20several%20UV%20spectral%20profiles%20at%20different%20locations%20along%20the%20slit.%20They%20exhibit%20enhanced%20emission%20with%20broad%20wings%2C%20and%20are%20non-Gaussian%2C%20mostly%20triangular-shaped%20profiles%2C%20similar%20to%20previous%20observations%20of%20plasmoid-mediated%20magnetic%20reconnection%20%28Innes%20et%20al.%201997%2C%202015%3B%20Rouppe%20van%20der%20Voort%20et%20al.%202017%29."},{"type":"image","file":"","url":"nuggetvideos/2021/10/26/pod_polito_vanessa_2021-10-26T21%3A53%3A23.861Z/Fig3.png","hash":"89c8377dc78bf0da76292faad4554775","mimeType":"image/png","caption":"Figure%203%3A%20Selected%20spectral%20profiles%20in%20the%20IRIS%20C%20II%201335%20%26Aring%3B%20%28upper%20left%29%2C%20Si%20IV%201394%20%26Aring%3B%20%28upper%20right%29%2C%20Si%20IV%201403%20%26Aring%3B%20%28lower%20left%29%2C%20and%20Mg%20II%20h%20and%20k%20lines%20at%20different%20locations%20along%20the%20slit."},{"type":"text","text":"From%20%5Cbegin%7Bequation%7DIRIS%5E2%5Cend%7Bequation%7D%20inversions%20of%20the%20observed%20IRIS%20Mg%20II%20spectral%20profiles%20we%20estimated%20that%20the%20highest%20temperatures%20are%20at%20the%20locations%20of%20NW%20magnetic%20elements%20and%20above%20the%20emerging%20flux%20region.%20This%20can%20be%20seen%20in%20the%20left%20panel%20of%20Figure%204.%20The%20temperature%20is%20higher%20along%20the%20loops%2C%20compared%20to%20the%20non-emerging%20quiet%20Sun%20flux%20regions.%20LOS%20plasma%20velocities%20within%20the%20emerging%20region%20are%20shown%20in%20the%20right%20panel%20and%20reveal%20that%20there%20are%20strong%20chromospheric%20upflows%20close%20to%20the%20loop%20tops%20%28about%20%E2%88%925%20km%2Fs%29%2C%20and%20downflows%20%28%E2%88%BC10%20km%2Fs%29%20at%20the%20positions%20of%20the%20footpoints.%20These%20results%20further%20establish%20our%20picture%20of%20plasma%20being%20pushed%20up%20to%20the%20chromosphere%20with%20plasma%20draining%20from%20the%20loops%20in%20the%20more%20vertically%20oriented%20footpoints."},{"type":"image","file":"","url":"nuggetvideos/2021/10/26/pod_polito_vanessa_2021-10-26T21%3A53%3A23.861Z/Fig4.png","hash":"1a9b83a32595c42d370b6b700f365b5f","mimeType":"image/png","caption":"Figure%204%3A%20%5Cbegin%7Bequation%7DIRIS%5E2%5Cend%7Bequation%7D%20inversions%20showing%20the%20temperature%20%28left%29%20and%20LOS%20velocity%20%28right%29%20maps%20at%20%5Cbegin%7Bequation%7Dlog_%7B10%7D%5Ctau_%7B500%7D%3D-5.8%5Cend%7Bequation%7D.%20The%20temperature%20map%20shows%20higher%20values%20within%20the%20flux%20emerging%20region.%20The%20LOS%20velocities%20reveal%20upflows%20around%20the%20loop%20tops%20and%20downflows%20that%20coincide%20with%20the%20footpoints%20and%20NW%20elements."},{"type":"text","text":"Our%20polarimetric%20observations%20obtained%20with%20SST%20in%20the%20Fe%20I%206173%20%26Aring%3B%2C%20Mg%20I%20b2%205173%20%26Aring%3B%20and%20Ca%20II%208542%20%26Aring%3B%20lines%20show%20three%20IN%20bipoles%20as%20they%20appear%20in%20the%20photosphere%20and%20rise%20up%20through%20the%20solar%20atmosphere.%20They%20provide%20the%20first%20direct%20observational%20evidence%20that%20IN%20fields%20are%20capable%20of%20reaching%20the%20chromosphere%2C%20and%20locally%20heating%20the%20upper%20solar%20atmosphere.%20According%20to%20our%20observations%2C%20it%20took%20about%20one%20hour%20for%20the%20IN%20fields%20to%20break%20through%20the%20ambient%20fields%20and%20emerge%20in%20the%20chromosphere.%20We%20estimated%20from%20the%20IRIS%20inversions%20of%20the%20Mg%20II%20h%20and%20k%20lines%20that%20the%20chromospheric%20temperature%20above%20the%20emerging%20IN%20fields%20rises%20up%20to%2010%20kK%20%28from%205-6%20kK%20in%20the%20very%20quiet%20regions%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, SoPh, 289, 2733</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021ApJ...911...41G/abstract\">Gosic, M., De Pontieu, B., Bellot Rubio, L. R., et al. 2021, ApJ, 911, 41</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...813...86I/abstract\">Innes, D. E., Guo, L.-J., Huang, Y.-M., & Bhattacharjee, A. 2015, ApJ, 813, 86</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1997Natur.386..811I/abstract\">Innes, D. E., Inhester, B., Axford, W. I., & Wilhelm, K. 1997, Natur, 386, 811</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014Sci...346C.315P/abstract\">Peter, H., Tian, H., Curdt, W., et al. 2014, Sci, 346, 1255726</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...851L...6R/abstract\">Rouppe van der Voort, L., De Pontieu, B., Scharmer, G. B., et al. 2017, ApJL, 851, L6</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...875L..18S/abstract\">Sainz Dalda, A., de la Cruz Rodriguez, J., De Pontieu, B., & Gosic, M. 2019, ApJL, 875, L18</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2003SPIE.4853..341S/abstract\">Scharmer, G. B., Bjelksjo, K., Korhonen, T. K., Lindberg, B., & Petterson, B. 2003a, in Innovative Telescopes and Instrumentation for Solar Astrophysics, eds. S. L. Keil, & S. V. Avakyan, Proc. SPIE, 4853, 341</a>","",""],"pubDate":"2021-11-10T20:10:09.592Z"},{"id":"pod_polito_vanessa_2021-09-21T16:49:25.122Z","submitter":"","author":"Pradeep Kayshap","status":"published","creation-date":"2021-09-21T16:49:25.127Z","last-modified-date":"2021-10-13T18:51:47.273Z","credit":"Vellore Institute of Technology - VIT Bhopal University, Kothri Kalan, Astha, M.P., India","title":"Homologous surges as seen by IRIS","contentBlocks":[{"type":"text","text":"High-resolution%20IRIS%20spectral%20observations%20in%20the%20Mg%20II%20k%202796.35%20%26Aring%3B%20and%20h%202803.35%20%26Aring%3B%2C%20Si%20IV%201402.77%20%26Aring%3B%2C%20and%20O%20IV%201401.15%20%26Aring%3B%20lines%20%28De%20Pontieu%20et%20al.%202014%29%20were%20used%20to%20analyze%20six%20homologs%20surges%2C%20which%20occurred%20on%20July%207%2C%202014%20near%20the%20limb%20%28Figure%201%29.%20The%20peak%20of%20the%20last%20surge%20is%20displayed%20in%20panel%20A%20along%20with%20the%20intensity-time%20map%20%28panel%20B%29%20obtained%20in%20the%20IRIS%2FSJI%201330%20%26Aring%3B%20filter.%20Further%2C%20panels%20C1%20to%20C5%20show%20Si%20IV%20and%20O%20IV%20spectral%20profiles%20at%20five%20different%20locations%20within%20the%20surge%20plasma%2C%20which%20are%20indicated%20by%20different%20slits%20in%20panel%20A.%20Despite%20being%20optically%20thin%2C%20we%20find%20that%20both%20lines%20show%20double%20peaks%20at%20all%20locations%20%28except%20the%20middle%20position%20which%20is%20a%20single%20peak%20profile%29%2C%20and%20are%20fitted%20by%20a%20double%20Gaussian%20function%20%28except%20panel%20C3%29.%20Interestingly%2C%20one%20peak%20of%20the%20Si%20IV%20line%20remains%20around%20-100%20km%2Fs%20for%20all%20five%20profiles%20while%20the%20other%20peak%20shows%20the%20change%20from%20red-shifts%20%28panel%20C1%29%20to%20blue-shifts%20%28panel%20C5%29%20as%20we%20move%20across%20the%20surge.%20The%20rest%20positions%20of%20Si%20IV%20and%20O%20IV%20are%20displayed%20by%20vertical%20blue%20and%20red%20dashed%20lines%2C%20respectively.%20A%20similar%20behavior%20is%20also%20found%20for%20the%20O%20IV%20line%20which%20is%20displayed%20in%20the%20same%20panels%20%28solid%20red%20curve%29.%20We%20suggest%20that%20the%20stationary%20component%20is%20a%20result%20of%20translation%20motions%20as%20the%20surge%20plasma%20is%20ascending%20up%2C%20while%20the%20variable%20peak%20occurs%20because%20of%20the%20rotating%20motion%20of%20surge%20plasma.%20We%20found%20that%20all%20other%20surges%20also%20show%20a%20similar%20behavior%2C%20and%20we%20conclude%20that%20there%20is%20a%20prevalence%20of%20rotating%20motions%20in%20these%20homologous%20surges."},{"type":"image","file":"","url":"nuggetvideos/2021/09/21/pod_polito_vanessa_2021-09-21T16%3A49%3A25.122Z/Nugget_2.png","hash":"2feabc60d6a135f9a85058d40dfa4fee","mimeType":"image/png","caption":"Figure%201%3A%20The%20strongest%20surge%20out%20of%20the%20six%20homologous%20surges%20%28panel%20A%29%20with%20five%20locations%20highlighted%20%28see%20colored%20slits%29%20and%20an%20intensity-time%20map%20%28panel%20B%29%20using%20IRIS%2FSJI%201330%20%26Aring%3B%20observations.%20The%20panels%20C1%20to%20C5%20display%20the%20Si%20IV%20and%20O%20IV%20spectral%20profiles%20from%20the%20selected%20five%20locations%20along%20with%20their%20rest%20positions%2C%20i.e.%2C%20blue%20and%20red-dashed%20lines%20for%20Si%20IV%20and%20O%20IV%2C%20respectively.%20We%20have%20fitted%20both%20the%20profiles%20with%20double%20Gaussians%20%28solid%20blue%20and%20red%20lines%20Si%20IV%20and%20O%20IV%2C%20respectively%29.%20We%20find%20that%20one%20peak%20remains%20at%20constant%20velocity%20while%20the%20Doppler%20shift%20of%20the%20other%20peak%20ranges%20from%20red%20to%20blue%20shifts."},{"type":"text","text":"We%20have%20estimated%20the%20Mg%20II%20k%2Fh%20ratio%20%28Rkh%29%2C%20Doppler%20velocity%2C%20and%20width%20maps%20for%20the%20complete%20observations%20%28covering%20all%20six%20surges%29%20which%20are%20shown%20in%20panels%20A%2C%20B%2C%20and%20C%20of%20Figure%202.%20The%20blue%20shifts%20dominate%20in%20the%20first%20half%20of%20all%20surges%2C%20and%20the%20Rkh%20is%20less%20than%202.0%2C%20suggesting%20that%20the%20Mg%20II%20resonance%20lines%20may%20be%20formed%20under%20optically%20thick%20conditions%20during%20the%20upflow%20phase%20of%20these%20surges.%20The%20second%20half%20of%20the%20surge%20is%20dominated%20by%20redshifts%2C%20and%20interestingly%2C%20the%20Rkh%20is%20greater%20than%202.0%2C%20i.e.%2C%20now%2C%20the%20line%20may%20be%20formed%20under%20optically%20thin%20conditions.%20The%20values%20of%20Rkh%20increase%20with%20the%20Doppler%20velocity%20pattern%20%28i.e.%2C%20from%20blueshift%20to%20redshifts%29%20and%20width%20pattern%20of%20each%20surge%20%28i.e.%2C%20widths%20of%20the%20lines%20decrease%20over%20the%20lifetime%20of%20each%20surge%29."},{"type":"image","file":"","url":"nuggetvideos/2021/09/21/pod_polito_vanessa_2021-09-21T16%3A49%3A25.122Z/Figure_Two.png","hash":"610c254b84b09deb854244edd7cdbc20","mimeType":"image/png","caption":"Figure%202%3A%20Mg%20II%20k%20to%20h%20ratio%20%28Rkh%3B%20panel%20a%29%2C%20Doppler%20velocity%20%28panel%20b%29%2C%20and%20width%20maps%20%28panel%20c%29%20of%20the%20Mg%20II%20k%202796.35%20%26Aring%3B%20line%20are%20displayed%20here.%20In%20the%20upflow%20phases%20of%20all%20surges%2C%20the%20Rkh%20is%20less%20than%20two%20%28i.e.%2C%20suggestive%20of%20optically%20thick%20conditions%29%20while%20Rkh%20becomes%20more%20than%202%20%28i.e.%2C%20the%20line%20may%20be%20formed%20under%20optically%20thin%20conditions%29%20during%20the%20downflow%20phases%20of%20all%20surges.%20The%20Gaussian%20width%20is%20high%20in%20the%20initial%20phases%20and%20decreases%20as%20time%20progress%20for%20each%20surge%2C%20i.e.%2C%20the%20Rkh%20increases%20as%20the%20line%20width%20decreases.%20On%20the%20right%20side%2C%20we%20show%20he%20Mg%20II%20k%20and%20h%20line%20profiles%2C%20which%20are%20single%20peaked%20profiles%20being%20formed%20in%20the%20optically%20thick%20atmosphere."},{"type":"text","text":"The%20height-time%20%28HT%29%20diagrams%20from%20IRIS%2FSJI%201330%20%26Aring%3B%2C%20SDO%2FAIA%20304%20%26Aring%3B%2C%20171%20%26Aring%3B%2C%20and%2094%20%26Aring%3B%20%28see%20right%20column%20of%20Figure%203%29%20are%20produced%20using%20the%20displayed%20slits%20%28see%3B%20left-column%20of%20figure%203%29.%20All%20surges%20are%20highlighted%20in%20the%20SJI-1330%20%26Aring%3B%20and%20AIA-304%20%26Aring%3B%20HT%20diagrams.%20We%20have%20drawn%20several%20slits%20highlighting%20the%20up%20flow%20and%20downfall%20phases%20of%20each%20surge%20to%20estimate%20various%20properties%20of%20the%20surges%2C%20namely%2C%20upflow%20and%20downflow%20velocities%2C%20lifetime%2C%20acceleration%2C%20and%20deceleration.%20It%20is%20found%20the%20homologous%20surges%20exhibit%20a%20large%20range%20of%20these%20parameters.%20We%20did%20not%20find%20signatures%20of%20the%20surges%20in%20the%20high-temperature%20channels%20of%20AIA%2C%20namely%2C%20171%20%26Aring%3B%20and%20304%20%26Aring%3B."},{"type":"image","file":"","url":"nuggetvideos/2021/09/21/pod_polito_vanessa_2021-09-21T16%3A49%3A25.122Z/Figure_Three.png","hash":"fdfa54fb3be55c09f41e8a2e5156b0c0","mimeType":"image/png","caption":"Figure%203%3A%20IRIS%2FSJI%201330%20%26Aring%3B%20%28panel%20a%29%2C%20AIA%20304%20%26Aring%3B%20%28panel%20b%29%2C%20171%20%26Aring%3B%20%28panel%20c%29%2C%20and%2094%20%26Aring%3B%20%28panel%20d%29%20images%20of%20the%20surges%20with%20overlaid%20the%20position%20of%20the%20slits%20we%20used%20to%20obtain%20the%20HT%20diagrams%20%28left%20panels%29.%20We%20also%20draw%20different%20slits%20in%20the%20HT%20diagrams%20of%20each%20surge%20%28see%3B%20panels%20e%20and%20f%29%20to%20estimate%20various%20kinematical%20properties.%20The%20surges%20are%20rarely%20visible%20in%20the%20AIA%20171%26Aring%3B%20and%20AIA%2094%20%26Aring%3B%20channels."},{"type":"text","text":"Finally%2C%20we%20have%20performed%20a%20differential%20emission%20measure%20%28DEM%29%20analysis%20for%20all%20surges%20using%20the%20software%20developed%20by%20Cheung%20et%20al.%20%282015%29.%20We%20show%20here%20the%20DEM%20distribution%20from%20the%20base%20%28black%20histogram%29%20and%20spire%20%28blue%20histogram%29%20of%20all%20six%20surges%20%28Figure%204%29.%20The%20footpoints%20of%20the%20surges%20show%20cool%20%28log%20T%2FK%20%7E%206.37%29%20and%20hot%20components%20%28log%20T%2FK%20%7E%206.91%29%2C%20while%20the%20spires%20of%20surges%20only%20show%20cool%20components.%20Hence%2C%20the%20presence%20of%20hot%20components%20only%20at%20the%20base%20of%20surges%20suggests%20heating%20in%20that%20location."},{"type":"image","file":"","url":"nuggetvideos/2021/09/21/pod_polito_vanessa_2021-09-21T16%3A49%3A25.122Z/Nugget_7.png","hash":"f0f80c00799c5f2629d7e124ccc46a6","mimeType":"image/png","caption":"Figure%204%3A%20DEM%20distributions%20at%20the%20base%20%28black%20histogram%29%20and%20spire%20%28blue%20histogram%29%20of%20all%20surges.%20We%20see%20two%20peaks%20at%20the%20base%20of%20surge%20%28i.e.%2C%20one%20peak%20in%20cool%20temperature%20regime%20while%20another%20peak%20in%20hot%20temperature%20regime%29%2C%20which%20are%20fitted%20by%20two%20Gaussian%20%28solid%20black%20curve%29%20lines.%20The%20DEM%20distribution%20of%20the%20spire%20region%20from%20each%20surge%20shows%20only%20a%20cool%20temperature%20peak%2C%20which%20is%20fitted%20by%20a%20single%20Gaussian%20%28solid%20blue%20curve%29."},{"type":"text","text":"It%20is%20the%20first%20time%20that%20surge%20emission%20is%20analyzed%20in%20the%20Mg%20II%20h%20and%20k%2C%20and%20O%20IV%20spectral%20lines.%20Earlier%2C%20only%20one%20work%20%28i.e.%2C%20N%26oacute%3Bbrega-Siverio%20et%20al.%202017%29%20has%20reported%20surge%20emission%20in%20Si%20IV.%20We%20find%20that%20the%20rotating%20motion%20is%20present%20in%20all%20surges%20along%20with%20heating%20signatures%20near%20the%20base%20of%20the%20surges.%20The%20presence%20of%20a%20heated%20base%20with%20rotating%20motion%20may%20suggest%20the%20occurrence%20of%20magnetic%20reconnection%20near%20the%20bases%20of%20surges%20as%20suggested%20by%20Fang%20et%20al.%20%282014%29%20and%20Kayshap%20et%20al.%20%282018%29.%20We%20suggest%20that%20this%20magnetic%20reconnection%20is%20responsible%20for%20the%20formation%20of%20these%20surges.%20In%20general%2C%20the%20Rkh%20is%20high%20in%20the%20homologous%20surges%20as%20compared%20to%20other%20features%20%28e.g.%2C%20flare%20emission%20%5BKerr%20et%20al.%202015%5D%20and%20filament%20eruption%20%5BHarra%20et%20al.%202014%5D%29.%20Please%20see%20Kayshap%20et%20al.%20%282021%29%20for%20the%20full%20details%20of%20this%20works."}],"references":["Cheung M. C. M., Boerner P., Schrijver C. J., Testa P., Chen F., Peter H., Malanushenko A., ApJ, 807, 143 (2015)","De Pontieu, B., Title, A. M., Lemen, J. R., et al. Solar Physics, 289, 2733 (2014)","Harra L. K., Matthews S. A., Long D. M., Doschek G. A., De Pontieu B., ApJ, 792, 93 (2014)","Kerr G. S., Simões P. J. A., Qiu J., Fletcher L., A&A, 582, A50 (2015)","Leenaarts J., Pereira T. M. D., Carlsson M., Uitenbroek H., De Pontieu B., ApJ, 772, 90 (2013)","Nóbrega-Siverio D., Martínez-Sykora J., Moreno-Insertis F., Rouppe van der Voort L., ApJ, 850, 153 (2017)","Fang, Fang, Fan, Yuhong, McIntosh, Scott W, ApJL, 789, 19 (2014)","Kayshap, P., Murawski, K., Srivastava, A.K., Dwivedi, A.K., A&A, 616, 99 (2018)","Kayshap, P., Singh Payal, Rajdeep, Tripathi, Sharad C., Padhy, Harihara, MNRAS, 505, 5311 (2021)",""],"pubDate":"2021-10-13T18:52:08.957Z"},{"id":"pod_polito_vanessa_2021-08-19T19:00:20.335Z","submitter":"Katharine Reeves","author":"Katharine K. Reeves [1] , Vanessa Polito [2,3] , Bin Chen [4] , Giselle Galan [1,5], Sijie Yu [4] , Wei Liu [2,3,6], and Gang Li [7]","status":"published","creation-date":"2021-08-19T19:00:20.343Z","last-modified-date":"2021-09-13T19:45:07.775Z","credit":"[1] Harvard-Smithsonian Center for Astrophysics, [2] Bay Area Environmental Research Institute, [3] Lockheed Martin Solar and Astrophysics Laboratory, [4] Center for Solar-Terrestrial Research, New Jersey Institute of Technology, [5] Department of Physics, Massachusetts Institute of Technology, [6] W.W. Hansen Experimental Physics Laboratory, Stanford University, [7] Department of Space Science and CSPAR, University of Alabama in Huntsville","title":"Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar Flare","contentBlocks":[{"type":"text","text":"On%20September%2010%202017%2C%20an%20X8%20flare%20and%20an%20associated%20spectacular%20eruption%20occurred%20on%20the%20west%20limb%20of%20the%20Sun.%20%20This%20event%20was%20observed%20by%20IRIS%2C%20AIA%2C%20EOVSA%20and%20Hinode.%20%20The%20IRIS%20pointing%20was%20just%20south%20of%20the%20main%20cusp-shaped%20loop%20structure%20visible%20in%20AIA%2C%20but%20it%20did%20capture%20most%20of%20the%20flare%20arcade%20on%20the%20limb%2C%20as%20shown%20in%20Figure%201.%20%20Shortly%20after%20the%20eruption%2C%20at%2015%3A55%20UT%2C%20microwave%20emission%20from%20EOVSA%20extends%20south%20from%20the%20bright%20flare%20loops%2C%20as%20seen%20in%20the%20top%20panel%20of%20Figure%201.%20At%20this%20time%2C%20there%20is%20some%20faint%20emission%20in%20the%20AIA%20131%20%26Aring%3B%20channel%20close%20to%20the%20limb%2C%20and%20some%20strands%20of%20emission%20in%20the%20IRIS%201330%20%26Aring%3B%20channel%20that%20look%20similar%20to%20coronal%20rain.%20As%20the%20eruption%20progresses%20%28lower%20panels%20of%20Figure%201%29%2C%20faint%2C%20diffuse%20emission%20is%20seen%20extending%20to%20the%20south%20of%20the%20bright%20flare%20arcade%20in%20the%20AIA%20131%20%26Aring%3B%20and%20193%20%26Aring%3B%20channels%20%28and%20also%20in%20the%20AIA%2094%20%26Aring%3B%20and%20335%20%26Aring%3B%20channels%2C%20which%20are%20not%20shown%29%2C%20and%20in%20the%20IRIS%201330%20%26Aring%3B%20SJI%20image."},{"type":"image","file":"","url":"nuggetvideos/2021/08/19/pod_polito_vanessa_2021-08-19T19%3A00%3A20.335Z/fig1.jpg","hash":"23edcb8ba7749c46547c04a23fe0d156","mimeType":"image/jpeg","caption":"Figure%201%3A%20Summary%20of%20AIA%20and%20IRIS%20images%3A%20The%20AIA%20131%20%26Aring%3B%2C193%20%26Aring%3B%20and%20IRIS%20SJI%201330%20%26Aring%3B%20channels%20during%20the%20flare.%20White%20contours%20show%20EOVSA%20microwave%20emission%20at%202.9%20GHz%20at%2050%25%2C%2075%25%2C%20and%2090%25%20intensity.%20The%20yellow%20and%20white%20boxes%20show%20the%20region%20of%20IRIS%20and%20EIS%20slit%20coverage%20examined%20in%20this%20work%2C%20and%20the%20yellow%20stars%20and%20white%20diamond%20show%20the%20locations%20of%20blue-shifted%20regions."},{"type":"text","text":"We%20examine%20in%20detail%20the%20data%20from%20the%20IRIS%20Fe%20XXI%20line%2C%20which%20is%20a%20coronal%20line%20that%20is%20formed%20at%20about%2010%20MK.%20%20For%20the%20IRIS%20Fe%20XXI%20data%2C%20a%20Gaussian%20is%20fit%20to%20the%20spectrum%20in%20every%20pixel%20along%20the%20slit%2C%20%20and%20Figure%202%20shows%20the%20intensity%2C%20%20the%20Doppler%20velocity%20and%20the%20non-thermal%20velocity%20for%208-step%20rasters.%20During%20the%20period%20from%2016%3A05%20-%2016%3A15%20UT%2C%20we%20find%20that%20faint%20blue-shifted%20regions%20appear%20at%20the%20top%20of%20the%20flare%20loops%2C%20indicating%20plasma%20flows%20of%2020-60%20km%2Fs.%20Loop%20top%20regions%20with%20blue%20shifts%20shown%20in%20Figure%202%20oscillate%20in%20Doppler%20shift%20as%20a%20function%20of%20time%2C%20as%20shown%20in%20Figure%203.%20The%20observed%20periods%20are%20fairly%20similar%2C%20on%20the%20order%20of%20400%20s%2C%20and%20there%20is%20no%20obvious%20correlation%20between%20the%20period%20of%20the%20oscillation%20and%20loop%20length%2C%20which%20rules%20out%20standing%20slow%20mode%20waves%20as%20the%20mechanism%20for%20the%20oscillation."},{"type":"image","file":"","url":"nuggetvideos/2021/08/19/pod_polito_vanessa_2021-08-19T19%3A00%3A20.335Z/fig2.jpg","hash":"e8a5046fda0b81adee1ca1b8a16ff631","mimeType":"image/jpeg","caption":"Figure%202.%20The%20intensity%20%28top%20row%29%2C%20the%20Doppler%20velocity%20%28middle%20row%29%2C%20and%20the%20nonthermal%20velocity%20%28bottom%20row%29%20for%20pixels%20along%20the%20slit%20in%20eight-step%20rasters%2C%20corresponding%20to%20the%20yellow%20box%20shown%20in%20Figure%201.%20The%20time%20given%20in%20the%20top%20row%20is%20the%20time%20for%20the%20first%20raster%20step.%20Color%20bars%20for%20each%20row%20are%20shown%20to%20the%20right.%20Boxes%20show%20the%20pixels%20that%20are%20averaged%20together%20to%20get%20average%20Doppler%20shifts%20in%20Figure%203."},{"type":"image","file":"","url":"nuggetvideos/2021/08/19/pod_polito_vanessa_2021-08-19T19%3A00%3A20.335Z/fig5.jpg","hash":"29239dc9232e6c3dc008697f485fce75","mimeType":"image/jpeg","caption":"Figure%203%3A%20IRIS%20Doppler%20shifts%20as%20a%20function%20of%20time%20for%20the%20pixels%20in%20the%20boxes%20shown%20in%20Figure%202.%20Times%20have%20been%20shifted%20so%20that%20the%20main%20blueshift%20for%20each%20time%20series%20occurs%20at%20the%20same%20time.%20For%20each%20plot%2C%20thin%20gray%20lines%20indicate%20the%20time%20series%20for%20each%20pixel%20in%20the%20box%2C%20averages%20for%20all%20the%20pixels%20in%20the%20box%20are%20shown%20as%20a%20thick%20black%20line%2C%20and%20a%20fit%20to%20the%20average%20using%20a%20damped%20oscillation%20is%20shown%20as%20a%20thick%20red%20line."},{"type":"text","tex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href=\"https://ui.adsabs.harvard.edu/abs/2020ApJ...895L..50C/abstract\">Chen, B. et al. The Astrophysical Journal Letters, Volume 895, Issue 2, id.L50, 10 pp. (2020)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...823..150T/abstract\">Takasao & Shibata, The Astrophysical Journal, Volume 823, Issue 2, article id. 150, 11 pp. (2016).</a>","","","","","","","",""],"pubDate":"2021-09-13T19:45:13.35Z"},{"id":"pod_polito_vanessa_2021-06-10T18:56:55.307Z","submitter":"(1) Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA, 94035, USA; (2) Lockheed Martin Solar and Astrophysics Laboratory, Building 252, 3251 Hanover Street, Palo Alto, CA, 94304, USA","author":"Magnus Woods (1,2)","status":"published","creation-date":"2021-06-10T18:56:55.312Z","last-modified-date":"2021-08-10T20:25:13.776Z","credit":"Alberto Sainz Dalda(1,2), Bart De Pontieu(2)","title":"Unsupervised Machine Learning for the Identification of Pre-flare Spectroscopic Signatures","contentBlocks":[{"type":"text","text":"In%20this%20study%20we%20use%20the%20unsupervised%20machine%20learning%20technique%20k-means%20clustering%20upon%20high%20resolution%20spectroscopic%20observations%20of%20the%20Mg%20II%20lines%20made%20by%20the%20Interface%20Region%20Imaging%20Spectrometer%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%20to%20try%20and%20identify%20pre-flare%20signatures%20in%20order%20to%20help%20elucidate%20the%20physical%20mechanisms%20behind%20flaring.%20%0A%0AThe%20k-means%20clustering%20algorithm%20%28MacQueen%20et%20al.%201967%29%20is%20widely%20used%20to%20categorise%20many%20types%20of%20data.%20We%20employed%20it%20to%20distinguish%20between%20spectra%20that%20occur%20widely%20in%20pre-flare%2C%20quiescent%20active%20region%20and%20quiet%20sun%20rasters%2C%20and%20those%20that%20appear%20in%20the%20pre-flare%20data%20sets%20only.%20%20We%20chose%20data%20from%208%20solar%20flares%20of%20X%20and%20M%20class%2C%20and%20selected%209%20rasters%20from%20each%20data%20set%2C%20starting%2040%20minutes%20prior%20to%20flaring%20in%205%20minute%20increments%20until%20flare%20onset%20as%20defined%20by%20the%20GOES%20flarelist.%20These%20data%20at%20each%20time%20step%20were%20then%20clustered%20alongside%20a%20large%20data%20set%20made%20up%20of%2032%20Quiescent%20AR%20data%20sets%20and%206%20Quiet%20Sun%20data%20sets.%20%0A%0AFigure%201%20shows%20the%20types%20of%20spectra%20that%20our%20clustering%20found%20only%20to%20occur%20in%20the%20pre-flare%20data%20sets.%20%20We%20can%20see%20that%20these%20eight%20broad%20categories%20are%20profiles%20which%20exhibit%3A%20%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines%3B%20double%20peaked%20k%20%26amp%3B%20h%20lines%2C%20with%20emission%20in%20the%20Mg%20II%20triplet%20line%3B%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%3B%20double%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%3B%20Broad%20Shouldered%20Mg%20II%20k%20%26amp%3B%20h%3B%20Broad%20Mg%20II%20k%20%26amp%3B%20h%3B%20Cosmic%20Ray%20hits%3B%20and%20the%20final%20group%20is%20of%20clusters%20which%20are%20irregular%20profiles%20with%20broad%20wings.%20%20Of%20these%208%20types%20of%20preflare%20cluster%2C%20the%20most%20common%20is%20spectra%20showing%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines.%20Profiles%20of%20this%20type%20comprise%20and%20average%20of%2076%25%20of%20all%20the%20identified%20preflare%20spectra%20at%20each%20timestep."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/clster_examples_v2.jpg","hash":"6ed0a249d9a67657ef997bc23dc7c20c","mimeType":"image/jpeg","caption":"Figure%201%3A%20This%20figure%20shows%20examples%20of%20the%208%20categories%20of%20pre-flare%20Representative%20Profiles.%20As%20before%2C%20the%20representative%20profile%20is%20shown%20in%20orange%2C%20with%20the%20black%20corresponding%20to%20the%20individual%20profiles%20that%20contribute%20to%20it."},{"type":"text","text":"The%20location%20of%20the%20pre-flare%20clusters%20was%20also%20investigated%2C%20as%20an%20example%20of%20this%20for%20one%20flare%20Figure%202%20shows%20the%20locations%20of%20all%20pre-flare%20clusters%20found%20at%20each%20time%20step%20overlayed%20onto%20the%20IRIS%20slit-jaw%20images.%20What%20we%20see%20when%20examining%20the%20locations%20of%20all%20the%20preflare%20clusters%20is%20that%20they%20predominately%20occur%20in%20regions%20where%20the%20flare%20ribbons%20will%20occur%20during%20the%20flare%20%28ribbon%20locations%20at%20flare%20peak%20are%20shown%20by%20the%20black%20contours%20in%20Figure%202%2C%20and%20by%20the%20green%20contours%20in%20Figure%203%29%20or%20are%20related%20with%20transient%20brightenings%20within%20the%20center%20of%20the%20active%20regions.%20Figure%203%2C%20for%20the%20same%20times%20and%20fields%20of%20view%2C%20shows%20the%20pre-flare%20clusters%20overlayed%20upon%20the%20corresponding%20SDO%20HMI%20line-of-sight%20magnetograms.%20From%20these%20we%20find%20that%20the%20majority%20of%20the%20pre-flare%20clusters%20broadly%20align%20with%20regions%20of%20intersection%20between%20the%20positive%20and%20negative%20magnetic%20field%20%28the%20white%20and%20black%20areas%20in%20the%20images%20respectively%29."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/dataset_3_locations.jpg","hash":"98e7c46274bdaccaea0f5e86d89ee81","mimeType":"image/jpeg","caption":"Figure%202%3A%20In%20this%20figure%20we%20see%20the%20locations%20of%20the%20pre-flares%20clusters%20found%20prior%20to%20the%20X2.1%20flare%20SOL2015-03-11T16%3A22%20at%20each%20of%20the%20nine%20time%20steps%20clustered.%20For%20each%20time%20step%20the%20corresponding%20IRIS%20SJI%20image%20is%20shown%2C%20with%20the%20location%20of%20the%20raster%20slit%20positions%20shown%20as%20the%20dotted%20lines.%20The%20location%20of%20the%20spectra%20in%20each%20individual%20cluster%20are%20shown%20in%20a%20unique%20colour%2C%20which%20are%20detailed%20by%20the%20neighbouring%20colour%20bar%20for%20each%20time%20step.%20The%20location%20of%20the%20flare%20ribbons%2C%20determined%20at%20the%20peak%20time%20of%20the%20flare%20are%20shown%20overlayed%20as%20black%20contours."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/dataset_3_locations_hmi_continuum.png","hash":"d45a389cf98a805073cb402ab8332466","mimeType":"image/png","caption":"Figure%203%3A%20In%20this%20figure%20we%20see%20the%20locations%20of%20the%20pre-flares%20clusters%20found%20prior%20to%20the%202015-03-11%20X2.1%20flare%20at%20each%20of%20the%20nine%20time%20steps%20clustered.%20For%20each%20time%20step%20the%20corresponding%20SDO%20HMI%20image%20is%20shown%2C%20with%20the%20location%20of%20the%20raster%20slit%20positions%20shown%20as%20the%20dotted%20lines.%20The%20location%20of%20the%20spectra%20in%20each%20individual%20cluster%20are%20shown%20in%20a%20unique%20colour%2C%20which%20are%20detailed%20by%20the%20neighbouring%20colour%20bar%20for%20each%20time%20step.%20The%20location%20of%20the%20flare%20ribbons%2C%20determined%20at%20the%20peak%20time%20of%20the%20flare%20are%20shown%20overlayed%20as%20green%20contours.%20Also%20overlain%20as%20contours%20are%20the%20locations%20of%20the%20penumbra%20%28purple%29%20and%20umbra%20%28grey%29."},{"type":"text","text":"We%20then%20decided%20to%20further%20investigate%20the%20conditions%20that%20could%20have%20produced%20the%20spectra%20showing%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines.%20From%20existing%20studies%20modelling%20Mg%20II%20profiles%20have%20found%20that%20in%20plage%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%20can%20be%20produced%20in%20a%20hot%2C%20dense%20chromosphere%2C%20with%20temperatures%20around%206500K%20%28Carlsson%20et%20al.%202015%29%2C%20while%20another%20study%20conducted%20under%20flaring%20conditions%20found%20that%20increased%20temperatures%2C%20densities%2C%20or%20velocities%20in%20the%20upper%20chromosphere%20can%20produce%20the%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%20%28Rubio%20da%20Costa%20et%20al.%202017%29.%20Recent%201D%20RHD%20modelling%20of%20these%20lines%20by%20Zhu%20et%20al.%20%282019%29%20also%20found%20that%20increased%20electron%20density%20in%20the%20upper%20chromosphere%20could%20produce%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20profiles.%20Additionally%2C%20this%20work%20found%20that%20these%20increased%20electron%20densities%20could%20result%20in%20profiles%20with%20single%20peaked%20%20Mg%20II%20UV%20triplet%20lines%2C%20while%20Pereira%20et%20al.%20%282015%29%20found%20that%20temperature%20increases%20in%20the%20upper%20chromosphere%20could%20produce%20these%20single%20peaked%20triplet%20lines.%20%0AWe%20conducted%20simultaneous%20inversions%20of%20the%20Mg%20II%20k%20%26amp%3B%20h%20lines%20and%20the%20C%20II%201334%20and%201335%20lines%20following%20the%20method%20of%20Sainz%20Dalda%202021%20in%20order%20to%20accurately%20investigate%20the%20thermodynamic%20conditions%20that%20produced%20these%20spectra.%20Figure%204%20shows%20the%20results%20of%20a%20typical%20spectra%20of%20this%20type%20that%20was%20inverted.%20We%20find%20that%20the%20model%20atmospheres%20of%20theses%20profiles%20show%20increases%20in%20both%20temperature%20and%20electron%20density%20in%20the%20chromosphere.%20This%20would%20seem%20to%20agree%20with%20the%20existing%20results%20above."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/nugget_inversion.png","hash":"5a030ef78d9e44fee5e95d176a0b6dae","mimeType":"image/png","caption":"Figure%204.%20This%20figure%20shows%20the%20input%20spectra%2C%20inversion%20fit%2C%20and%20resultant%20model%20atmospheres%20for%20a%20single%20peaked%20pre-flare%20Mg%20II%20spectrum.%20In%20each%20panel%20the%20upper%20and%20middle%20images%20show%20the%20observed%20C%20II%20and%20Mg%20II%20spectra%20%28purple%29%20respectively%20with%20the%20model%20fits%20overlaid%20%28black%29.%20The%20Mg%20II%20images%20also%20has%20a%20synthetic%20profile%20produced%20from%20the%20FALC%20model%20%28dashed-blue%29%20overlain.%20Two%20double-axes%20below%20show%20the%20parameters%20of%20the%20resultant%20model%20from%20the%20inversion%20of%20the%20observed%20profiles%20%28solid%20lines%29%20and%20for%20the%20FALC%20model%20%28dashed%20line%29%20used%20as%20the%20initial%20guess%20model%20in%20the%201st%20cycle%20of%20the%20inversion.%20The%20temperature%20and%20electron%20%28orange%20and%20blue%20respectively%29%20density%20are%20shown%20on%20the%20left%2C%20while%20microturbulence%20%28vturb%29%20and%20line-of-sight%20velocity%20%28vLOS%29%20are%20shown%20on%20the%20right%20%28purple%20and%20green%20respectively%29."},{"type":"text","text":"From%20both%20our%20inversions%20and%20observation%20results%2C%20we%20conclude%20that%20these%20pre-flare%20spectra%20which%20exhibit%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines%20are%20often%20seen%20up%20to%2040%20minutes%20prior%20to%20flaring%20and%20that%20these%20spectra%20are%20most%20likely%20produced%20during%20small%20scale%20heating%20events%20in%20the%20chromosphere."}],"references":["<a href=\"https://link.springer.com/article/10.1007/s11207-014-0485-y\">De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Solar Physics, 289, 2733 </a>","<a href=\"https://projecteuclid.org/ebooks/berkeley-symposium-on-mathematical-statistics-and-probability/Proceedings%20of%20the%20Fifth%20Berkeley%20Symposium%20on%20Mathematical%20Statistics%20and%20Probability,%20Volume%201:%20Statistics/chapter/Some%20methods%20for%20classification%20and%20analysis%20of%20multivariate%20observations/bsmsp/1200512992\">MacQueen J., et al. 1967, in Proceedings of the fifth Berkeley symposium on mathematical statistics and probability, Oakland, CA, USA </a>","<a href=\"https://iopscience.iop.org/article/10.1088/2041-8205/809/2/L30\">Carlsson, M., Leenaarts, J., & De Pontieu, B. 2015, ApJL, 809, L30 </a>","<a href=\"https://iopscience.iop.org/article/10.3847/1538-4357/aa6eaf\">Rubio da Costa, F., & Kleint, L. 2017, ApJ, 842, 82 </a>","<a href=\"https://iopscience.iop.org/article/10.3847/1538-4357/ab2238\">Zhu, Y., Kowalski, A. F., Tian, H., et al. 2019, The Astrophysical Journal, 879, 19 </a>","<a href=\"https://iopscience.iop.org/article/10.1088/0004-637X/806/1/14\">Pereira, T. M. D., Carlsson, M., De Pontieu, B., & Hansteen, V. 2015, ApJ, 806, 14 </a>","Sainz Dalda, A. in prep.","","",""],"pubDate":"2021-08-10T20:25:18.54Z"},{"id":"pod_polito_vanessa_2021-05-24T16:29:42.339Z","submitter":"(2) Rosseland Centre for Solar Physics, University of Oslo, P.O.Box 1029 Blindern, NO-0315 Oslo, Norway","author":"Sargam M. Mulay (1) and Lyndsay Fletcher (1,2)","status":"published","creation-date":"2021-05-24T16:29:42.344Z","last-modified-date":"2021-07-12T23:20:47.314Z","credit":"(1) School of Physics & Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK","title":"Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite","contentBlocks":[{"type":"text","text":"In%20this%20study%2C%20we%20observe%20molecular%20hydrogen%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%201333.79%20%26Aring%3B%20emission%20at%20the%20flare%20ribbons%20during%20different%20phases%20of%20the%20M7.3%20class%20solar%20flare%20observed%20by%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%3B%20De%20Pontieu%20et%20al.%202014%29%20on%20April%2018%2C%202014.%20The%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20line%20has%20a%20formation%20temperature%20of%204200%20K%20%28Innes%202008%29%20and%20its%20emission%20is%20produced%20through%20the%20photo-excitation%20%28fluorescence%29%20process%20by%20ultraviolet%20%28UV%29%20radiation%20from%20the%20IRIS%20Si%20IV%201402.77%20%26Aring%3B%20line.%20This%20work%20provides%20a%20unique%20view%20and%20plasma%20properties%20of%20the%20temperature%20minimum%20region%20%28TMR%29.%20High-resolution%20IRIS%20observations%20allow%20us%20to%20study%20the%20behavior%20and%20plasma%20properties%20of%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20at%20the%20flare%20ribbons%20during%20various%20phases%20of%20the%20flare%2C%20the%20correlation%20between%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20the%20Si%20IV%20emission%2C%20and%20the%20optical%20properties%20of%20the%20plasma%20to%20the%20outward-going%20radiation%2C%20using%20the%20ratio%20of%20the%20two%20Si%20IV%20line%20intensities."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_698.png","hash":"515b3773b7ff3819609695d5a1ae3658","mimeType":"image/png","caption":"Figure%201%20-Left%20panel%3A%20GOES%20X-ray%20fluxes%20and%20their%20derivative%20for%20an%20M7.3%20flare.%20The%20plasma%20parameters%20from%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20were%20obtained%20for%20the%20time%20slot%20marked%20by%20dashed%20lines.%20Right%20panel%3A%20The%20southern%20flare%20ribbon%20is%20observed%20in%20the%20IRIS%20SJI%20Si%20IV%20filter.%20The%20two%20regions%20of%20a%20southern%20flare%20ribbon%20are%20labeled%20as%20Ribbon%201%20%28R1%29%20and%202%20%28R2%29."},{"type":"text","text":"Emission%20from%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20were%20observed%20throughout%20the%20flare%20evolution.%20At%20R1%2C%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20was%20visible%20only%20when%20emission%20from%20Si%20IV%20was%20bright.%20We%20observed%20that%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20is%20strongest%20during%20the%20flare%20impulsive%20phase%2C%20dims%20during%20the%20GOES%20peak%2C%20and%20brightens%20again%20during%20the%20gradual%20phase.%20At%20R2%2C%20the%20Si%20IV%20emission%20was%20strong%20but%20at%20the%20same%20time%20and%20location%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20line%20was%20faint.%20This%20might%20be%20caused%20by%20the%20fact%20that%20the%20opacity%20of%20the%20chromosphere%20at%20the%20R2%20location%20was%20higher%20than%20that%20at%20the%20R1%20location.%20We%20noted%20that%20R1%20crosses%20a%20plage%20region%2C%20whereas%20R2%20crosses%20a%20spot%20penumbra%2C%20which%20is%20expected%20to%20have%20different%20temperature%2C%20density%20and%20hence%2C%20opacity%20structures."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_683.png","hash":"1cd5433cfece7fd95eb1a7ec66663e8e","mimeType":"image/png","caption":"Figure%202%20%E2%80%93%20Left%20and%20middle%20panels%20%E2%80%93%20%28a%29%20%26amp%3B%20%28d%29%20spectral%20images%20created%20by%20summing%20the%20intensities%20over%20the%20range%20of%20wavelengths%201333.76%20-%201333.87%20%26Aring%3B%2C%20and%201402.5%20-%201403.6%20%26Aring%3B.%20%28b%29%20%26amp%3B%20%28e%29%20spectral%20images%20formed%20at%20the%20single%20%28peak%29%20wavelength%20for%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines.%20Right%20panel%3A%20Example%20spectra%20of%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20along%20with%20Gaussian%20fit%20components."},{"type":"text","text":"The%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20were%20broad%20%28see%20Fig.%202%2C%20right%20panel%29.%20We%20measured%20non-thermal%20speeds%20in%20the%20range%20of%207-18%20km%2Fs%20in%20the%20molecular%20line%2C%20whereas%20its%20Doppler%20shifts%20were%20consistent%20with%20zero%20within%20the%20errors%2C%20indicating%20negligible%20bulk%20flows%20along%20the%20line-of-sight.%0AWe%20studied%20the%20correlation%20between%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20emission%20by%20plotting%20the%20light%20curves%20for%20both%20ribbons.%20For%20R1%2C%20the%20overall%20pattern%20of%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20intensity%20variation%20is%20very%20similar%20to%20that%20of%20Si%20IV%20and%20showed%20many%20of%20the%20same%20small-scale%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href=\"https://ui.adsabs.harvard.edu/abs/1979MNRAS.187..463B/abstract\">Bartoe J.-D. F., et al. MNRAS, 187, 463 (1979)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...810....4B/abstract\">Brannon S. R., Longcope D. W., Qiu J., ApJ, 810, 4 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...810...45B/abstract\">Brosius J. W., Daw A. N., ApJ, 810, 45 (2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...830..101B/abstract\">Brosius J. W., Daw A. N., Inglis A. R., ApJ, 830, 101 (2016)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\">De Pontieu B., et al., Sol. Phys., 289, 2733 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1977Natur.270..326J/abstract\">Jordan C., et al., Nature, 270, 326 (1977)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1978ApJ...226..687J/abstract\">Jordan C., et al., ApJ, 226, 687 (1978)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...855..134J/abstract\">Jaeggli S. A., Judge P. G., Daw A. N., ApJ, 855, 134 (2018)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021MNRAS.504.2842M/abstract\">Mulay S. M., Fletcher L., MNRAS, 504, 2842 (2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1986ApJS...61..801S/abstract\">Sandlin G. D., et al., ApJS, 61, 801 (1986)</a>"],"pubDate":"2021-07-12T23:20:52.484Z"},{"id":"pod_polito_vanessa_2021-05-18T22:48:19.507Z","submitter":"1. Department of Physics, DSB Campus, Kumaun University, Nainital, India 2. LESIA, Observatoire de Paris, Meudon, France 3. Astronomical Institute of the Czech Academy of Sciences, Ondrejov, Czech Republic","author":"Reetika Joshi (1)","status":"published","creation-date":"2021-05-18T22:48:19.512Z","last-modified-date":"2021-06-14T16:54:35.495Z","credit":"Brigitte Schmieder (2), Guillaume Aulanier (2), Petr Heinzel (3), Ramesh Chandra (1)","title":"Sandwich model for multi thermal atmosphere of a mini-solar flare during jet reconnection","contentBlocks":[{"type":"text","text":"The%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%20has%20revealed%20several%20transient%20small-scale%20phenomena%20in%20the%20solar%20atmosphere%2C%20such%20as%20%0AIRIS%20bombs%20%28IBs%2C%20Peter%20et%20al.%2C%202014%2C%20Grubecka%20et%20al.%2C%202016%29%20subclass%20of%20solar%20Ultraviolet%20%28UV%29%20bursts%20%28Young%20et%20al.%2C%202018%2C%20De%20Pontieu%2C%20et%20al.%2C%202021%29%2C%20explosive%20events%20%28Kim%20et%20al.%202015%29%2C%20blow%20jets%20%28Shen%20et%20al.%202017%29%2C%20and%20bidirectional%20outflow%20jets%20%28Ruan%20et%20al.%2C%202019%29.%20Solar%20jets%20are%20commonly%20observed%20with%20IRIS%20and%20the%20multi-wavelength%20AIA%20telescope.%20The%20characteristics%20of%20such%20jets%20can%20vary%3A%20their%20velocity%20can%20reach%20between%20100%20and%20%20400%20km%2Fs%20and%20their%20typical%20length%20can%20range%20between%2050%20and%20100%20Mm%20%28Joshi%20et%20al.%202020a%29.%20The%20IRIS%20spectroscopic%20and%20imaging%20observations%20of%20jets%20have%20also%20revealed%20bidirectional%20outflows%20in%20transition%20region%20lines%20at%20the%20base%20of%20the%20jets%2C%20thereby%20implying%20explosive%20magnetic%20reconnection%20processes.%0A%0AIn%20this%20study%2C%20we%20analysed%20the%20fine%20structure%20and%20dynamics%20of%20the%20plasma%20at%20the%20base%20of%20a%20jet%20forming%20a%20mini-flare%20%28GOES%20B6.7%29%20between%20two%20emerging%20magnetic%20fluxes%20%28EMFs%29%2C%20as%20observed%20with%20IRIS%20and%20SDO%20%28Joshi%20et%20al.%2C%202021%29.%20On%20March%2022%2C%202019%20between%2001%3A43%3A27%20UT%20and%2002%3A42%3A30%20UT%2C%20IRIS%20was%20targeting%20the%20base%20of%20the%20jet%20%20in%20the%20NOAA%20AR%2012736.%20When%20the%20jet%20appeared%2C%20IRIS%20acquired%20slit%20jaw%20images%20%28SJIs%29%20in%20two%20passbands%3A%201330%20%26Aring%3B%2C%20dominated%20by%20the%20C%20II%20lines%2C%20and%202796%20%26Aring%3B%2C%20dominated%20by%20the%20Mg%20II%20k%20line%20%28Joshi%20et%20al.%2C%202020b%29.%20The%20jet%2C%20which%20was%20accompanied%20by%20a%20cool%20surge%2C%20was%20observed%20for%20one%20hour%20in%20different%20AIA%20and%20IRIS%20wavebands.%20An%20overview%20of%20the%20AR%2012736%20with%20the%20mini-flare%20is%20presented%20in%20Fig.%201.%20Panel%20%28a%29%20shows%20the%20full%20disk%20image%20of%20the%20Sun%20and%20the%20AR%20under%20study%2C%20while%20panel%20%28b%29%20shows%20a%20zoom%20view%20of%20the%20304%20%26Aring%3B%20map%20overlaid%20with%20the%20HMI%20magnetic%20field%20contours%20of%20the%20emerging%20magnetic%20flux%20%28EMF%29.%20The%20initiation%20of%20the%20jet%20and%20surge%20occurred%20between%20the%20opposite%20polarities%20of%20the%20two%20EMFs%20%28panel%20%28b%29%29.%20This%20region%20is%20zoomed%20in%20panel%20%28c%29%2C%20which%20also%20shows%20the%20bright%20point%20at%20the%20footpoint%20of%20the%20jet.%20IRIS%20observed%20the%20AR%20with%20a%20four-step%20raster%20and%20the%20slit%20position%201%20crossed%20the%20reconnection%20region%20in%20the%20bright%20point."},{"type":"image","file":"","url":"nuggetvideos/2021/05/18/pod_polito_vanessa_2021-05-18T22%3A48%3A19.507Z/Screenshot 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PM.png","hash":"b3711a090fd0b77957197e3f75518c89","mimeType":"image/png","caption":"Fig.%201%3A%20Observations%20of%20the%20solar%20jet%20and%20surge%20in%20AIA%20304%20%26Aring%3B%20and%20IRIS%20SJI%20CII%201330%20%26Aring%3B%20on%20March%2022%2C%202019.%20Panel%20a%20shows%20the%20full%20disk%20image%20of%20the%20Sun%2C%20and%20the%20blue%20rectangular%20box%20the%20AR%20which%20is%20zoomed%20in%20panel%20b.%20In%20panel%20b%20the%20green%20contours%20represent%20positive%20magnetic%20polarity%20and%20blue%20contours%20negative%20magnetic%20polarity%20%28%2B%2F-%20300%20Gauss%29.%20Magnetic%20reconnection%20occurred%20between%20two%20emerging%20magnetic%20flux%20%28EMF%29%20regions%20initiating%20the%20jet%20and%20surge.%20The%20reconnection%20site%20%28bright%20point%29%20is%20crossed%20by%20the%20IRIS%20slit%20position%201%20indicated%20by%20the%20green%20arrow%20in%20panel%20c."},{"type":"text","text":"Figure%202%20shows%20an%20overview%20of%20the%20spatio-temporal%20analysis%20of%20the%20IRIS%20spectra%20in%20the%20Mg%20II%2C%20C%20II%2C%20and%20Si%20IV%20lines.%20During%20the%20reconnection%2C%20the%20IRIS%20spectra%20of%20the%20mini-flare%20show%20absorption%20in%20line%20cores%20%28Fig.%202%20d-f%29%20corresponding%20to%20the%20dark%20material%20seen%20in%20the%20AIA%20304%20%26Aring%3B%20images%20%28see%20between%20the%20two%20arrows%20in%20Fig.%202%20a-c%29.%20This%20suggests%20the%20presence%20of%20cool%20plasma%20above%20hotter%20plasma.%20The%20Doppler%20velocities%20from%20the%20Mg%20II%20lines%20were%20computed%20using%20a%20cloud%20model%20technique.%20According%20to%20this%20technique%2C%20the%20Mg%20II%20large%20extended%20blueshift%20profiles%20have%20been%20interpreted%20as%20being%20due%20to%20the%20presence%20of%20two%20cool%20clouds%20over%20the%20reconnection%20site%20with%20velocities%20of%20around%20-300%20km%2Fs%20and%20-36%20km%2Fs%20respectively%20%28Fig.%203%20c%20in%20right%20panel%29.%20The%20large%20%20Si%20IV%20and%20C%20II%20line%20width%20indicates%20%20similar%20velocities%20%28Fig.%203%20a%2C%20b%29.%20%20We%20speculate%20that%20one%20part%20of%20the%20trapped%20cool%20material%20could%20have%20been%20ejected%20with%20a%20low%20velocity%20while%20the%20other%20part%20was%20ejected%20with%20a%20fast%20upwards%20velocity%20during%20approximately%20one%20minute.%20The%20presence%20of%20such%20cool%20plasma%20over%20the%20heated%20atmosphere%20at%20the%20reconnection%20site%20is%20also%20confirmed%20by%20the%20presence%20of%20%20photospheric%20lines%20%20%28Fe%20II%20and%20Ni%20II%29%20visible%20in%20absorption%20features%20across%20%20the%20Si%20IV%20profiles%20%28Fig.%203%20a%29.%20The%20presence%20of%20such%20lines%20superimposed%20on%20emission%20lines%20%20implies%20also%20%20that%20cool%20%20material%20is%20stacked%20on%20top%20of%20hot%20material."},{"type":"image","file":"","url":"nuggetvideos/2021/05/18/pod_polito_vanessa_2021-05-18T22%3A48%3A19.507Z/Screenshot 2021-05-23 at 8.53.20 PM.png","hash":"87de82eed0b98ee453c41cfbcfea1a06","mimeType":"image/png","caption":"Fig.%202%3A%20Jet%20reconnection%20base%20%28UV%20burst%20or%20mini-flare%29%20and%20jet%20evolution.%20First%20column%3A%20images%20in%20AIA%20304%20%26Aring%3B.%20Second%2C%20third%2C%20and%20last%20columns%20show%20IRIS%20spectra%20of%20the%20jet%20reconnection%20site%20%28UV%20burst%29%20at%20the%20slit%20position%201%20%28shown%20by%20cyan%20arrows%20in%20panel%20a-c%29%20in%20the%20Mg%20II%20k%2C%20C%20II%2C%20and%20Si%20IV%20lines%20respectively."},{"type":"text","text":"To%20explain%20these%20observations%2C%20we%20propose%20a%20stratification%20model%20for%20the%20white%20light%2C%20mini-flare%20atmosphere%20where%20multiple%20layers%20at%20different%20temperatures%20are%20found%20along%20the%20line%20of%20sight%20%28LOS%29%20in%20a%20reconnection%20current%20sheet%20%28Fig.%203%2C%20left%20panel%29.%20Emission%20in%20the%20temperature%20minimum%20region%20is%20also%20detected%20with%20the%20AIA%201600%20%26Aring%3B%20and%201700%20%26Aring%3B%20filters%2C%20confirming%20the%20presence%20of%20heating%20in%20the%20low%20atmosphere.%20The%20Mg%20II%20and%20C%20II%20lines%20are%20good%20diagnostics%20for%20detecting%20plasma%20at%20chromospheric%20temperature%20%28T%20%26lt%3B%2020000%20K%29%2C%20Si%20IV%20at%20transition%20region%20temperature.%20We%20identified%20bilateral%20outflows%20in%20these%20lines%20%20%28Fig.%202%20at%2002%3A04%3A28%20%20UT%29%20%20within%20a%20bald%20patch%20region%20%28BP-%20where%20the%20magnetic%20field%20lines%20are%20tangent%20to%20the%20solar%20surface%29%20in%20HMI%20vector%20magnetograms.%20The%20BP%20current%20sheet%20is%20transformed%20to%20an%20%26quot%3BX%26quot%3B-point%20current%20sheet%20during%20the%20reconnection%2C%20which%20is%20responsible%20for%20the%20hot%20plasma%20detected%20in%20the%20AIA%20filters%20%2894%20%26Aring%3B%20-%20211%20%26Aring%3B%29%2C%20as%20shown%20by%20the%20OHM%20MHD%20model%20%28Joshi%20et%20al.%2C%202020b%29.%20%20The%20presence%20of%20cool%20plasma%20above%20transition%20region%20temperature%20plasma%20in%20the%20reconnection%20site%20could%20be%20caused%20by%20the%20ejected%20cool%20clouds%20from%20the%20BP.%20We%20note%20that%20this%20event%20is%20embedded%20in%20the%20corona.%20This%20demonstrates%20the%20possibility%20of%20producing%20different%20velocities%20and%20temperatures%20across%20successive%20layers%20of%20the%20atmosphere%20in%20the%20current%20sheet.%20This%20is%20the%20first%20time%20that%20we%20could%20quantify%20the%20fast%20speed%20%28possibly%20super%20Alfv%26eacute%3Bnic%20flows%29%20of%20cool%20clouds%20which%20were%20ejected%20perpendicularly%20to%20the%20jet%20direction%20via%20the%20cloud%20model%20technique.%20We%20speculate%20that%20the%20ejected%20clouds%20originated%20from%20plasma%20which%20was%20inserted%20between%20the%20two%20EMFs%20in%20the%20BP%20before%20reconnection%20or%20that%20are%20caused%20by%20cool%20upflow%20material%20similar%20to%20a%20surge%20during%20reconnection."},{"type":"image","file":"","url":"nuggetvideos/2021/05/18/pod_polito_vanessa_2021-05-18T22%3A48%3A19.507Z/Screenshot 2021-05-23 at 8.54.57 PM.png","hash":"e1bca2e46521be11010e0faf8788f94","mimeType":"image/png","caption":"Fig.%203%3A%20Left%20panel%3A%20Model%20of%20multi-layers%20atmosphere%20of%20a%20mini-flare%20at%20the%20time%20of%20reconnection%20in%20a%20bald%20patch%20region.%20The%20LOS%20successively%20crosses%20cool%20and%20hot%20layers%20%28white%20for%20the%20temperature%20minimum%20region%2C%20yellow%20for%20chromosphere%20up%20to%20transition%20region%20temperatures%2C%20red%20for%20coronal%20temperatures%29.%20Right%20panel%3A%20Line%20profiles%20at%20the%20reconnection%20point%20in%20Si%20IV%2C%20C%20II%2C%20and%20in%20Mg%20II%20lines.%20The%20presence%20of%20photospheric%20lines%20viewed%20in%20absorption%20%28Ni%20II%201393.33%20%26Aring%3B%20and%20Fe%20II%201393.589%20%26Aring%3B%29%20are%20indicated%20by%20red%20arrows.%20Self-absorption%20of%20the%20Si%20IV%20line%20blended%20by%20a%20Fe%20II%20line%20is%20indicated%20by%20the%20black%20arrow%20in%20the%20top%20right%20panel."},{"type":"text","text":"This%20work%20is%20done%20in%20collaboration%20with%20%20Brigitte%20Schmieder%2C%20Akiko%20Tei%2C%20Guillaume%20Aulanier%2C%20Juraj%20L%26ouml%3Brin%C4%8D%26iacute%3Bk%2C%20Ramesh%20Chandra%2C%20Petr%20Heinzel%2C%20V%26eacute%3Bronique%20Bommier%20and%20published%20as%20%20Joshi%20et%20al.%2C%202020b%20%20and%20%20Joshi%20et%20al.%2C%202021."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2021SoPh..296...84D/abstract\">De Pontieu, B., Polito, V., Hansteen, V., et al., Sol. Phys., 296, 84(2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016A%26A...593A..32G/abstract\">Grubecka, M., Schmieder, B., Berlicki, A., et al., A&A, 593, A32(2016)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...639A..22J/abstract\">Joshi, R., Chandra, R., Schmieder, B., et al., A&A, 639, A22(2020a)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2020A%26A...642A.169J/abstract\">Joshi, R., Schmieder, B., Aulanier, G., Bommier, V., Chandra, R., A&A, 642, A169(2020b)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...645A..80J/abstract\">Joshi, R., Schmieder, B., Tei, A., et al., A&A, 645, A80(2021)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2015ApJ...810...38K/abstract\">Kim, Y.-H., Yurchyshyn, V., Bong, S.-C., et al., ApJ, 810, 38(2015)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014Sci...346C.315P/abstract\">Peter, H., Tian, H., Curdt, W., et al., Science, 346, 1255726(2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...883...52R/abstract\">Ruan, G., Schmieder, B., Masson, S., et al., ApJ, 883, 52(2019)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...851...67S/abstract\">Shen, Y., Liu, Y. D., Su, J., Qu, Z., & Tian, Z., ApJ, 851, 67(2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018SSRv..214..120Y/abstract\">Young, P. R., Tian, H., Peter, H., et al., Space Sci. Rev., 214, 120(2018)</a>"],"pubDate":"2021-06-10T18:49:18.957Z"},{"id":"pod_polito_vanessa_2021-04-21T16:35:18.398Z","submitter":"","author":"Patrick Antolin","status":"published","creation-date":"2021-04-21T16:35:18.403Z","last-modified-date":"2021-05-14T16:55:37.792Z","credit":"Paolo Pagano, Paola Testa, Antonino Petralia, Fabio Reale","title":"Nanojets of Coronal Heating","contentBlocks":[{"type":"text","text":"Coronal%20heating%20has%20been%20puzzling%20scientists%20for%20decades%20since%20its%20discovery%20more%20than%2080%20years%20ago.%20The%20million-degree%20inner%20corona%2C%20composed%20mainly%20of%20closed%20loop%20structures%2C%20reflects%20a%20mind-blowing%20multi-scale%20problem%20of%20magnetic%20energy%20conversion%20into%20heat.%20Two%20major%20heating%20categories%20have%20been%20proposed.%20MHD%20waves%20%28AC%20mechanisms%29%20constitute%20one%20of%20the%20groups%2C%20while%20the%20other%20is%20based%20on%20the%20slow%20build-up%20of%20magnetic%20stress%20and%20currents%20through%20the%20braiding%20of%20the%20magnetic%20field%2C%20eventually%20released%20through%20magnetic%20reconnection%20%28DC%20mechanisms%29.%20Parker%20et%20al.%201988%20envisioned%20that%20reconnection%20processes%20should%20occur%20continuously%20in%20the%20corona%20once%20critical%20current%20thresholds%20are%20reached%2C%20thereby%20releasing%20magnetic%20energy%20and%20producing%20impulsive%20intensity%20bursts%20known%20as%20nanoflares.%20While%20such%20small-scale%20%28on%20the%20order%20of%20%5Cbegin%7Bequation%7D%2010%5E%7B24%7D%20%5Cend%7Bequation%7D%20ergs%29%20nanoflare-like%20intensity%20bursts%20can%20now%20be%20observed%20with%20current%20instrumentation%20%28e.g.%20Testa%20et%20al.%202013%29%2C%20numerical%20modelling%20has%20shown%20that%20both%20AC%20and%20DC%20mechanisms%20are%20able%20to%20produce%20such%20features%20%28e.g.%20Antolin%20et%20al.%202008%29%2C%20thereby%20preventing%20discrimination%20between%20the%20two%20scenarios."},{"type":"image","file":"","url":"nuggetvideos/2021/04/21/pod_polito_vanessa_2021-04-21T16%3A35%3A18.398Z/fullfov_nanojet.png","hash":"a43c571f5f8c8adc7a77580899db6fbf","mimeType":"image/png","caption":"Fig.%201.%20Discovery%20of%20nanojets.%20%28Left%20panel%29%20Full%20disc%20AIA%20171%20%26Aring%3B%20image%20showing%20the%20IRIS%20field-of-view%20%28red%20square%29%20centred%20on%20an%20off-limb%20prominence%2Fcoronal%20rain%20complex.%20%28Middle%20panel%29%20Zoom-in%20onto%20the%20IRIS%2FSJI%20field-of-view.%20Fast%2C%20bursty%20and%20tiny%20jet-like%20structure%20termed%20%27nanojets%27%20are%20detected%20in%20a%20loop-like%20cool%20structure%20in%20the%20IRIS%2FSJI%201400%20%26Aring%3B%20channel%20%28inner%20zoomed-in%20region%29.%20The%20nanojets%20are%20peculiar%20in%20terms%20of%20their%20transverse%20direction%20with%20respect%20to%20the%20loop.%20They%20occur%20in%20isolation%20or%20in%20clusters.%20%28Right%20panel%29%20An%20image%20sequence%20in%20SJI%201400%20%26Aring%3B%20showing%20a%20nanojet%20cluster%20%28white%20arrows%29%2C%20accompanied%20by%20the%20ejection%20of%20downward-directed%20plasmoids%20%28green%20arrows%29."},{"type":"text","text":"In%20this%20work%20%28Antolin%20et%20al.%202021%29%2C%20the%20IRIS%20spectrograph%27s%20slit%20detected%20a%20unique%20feature%20of%20the%20DC%20heating%20mechanism.%20Observing%20off-limb%20at%20a%20prominence%2Fcoronal%20rain%20complex%2C%20IRIS%20observed%20the%20heating%20to%20multi-million%20degree%20temperatures%20of%20an%20initially%20cool%20loop-like%20structure%20attached%20to%20the%20prominence%20%28Fig.%201%29.%20A%20myriad%20small-scale%2C%20bursty%20events%20with%20nanoflare-like%20energies%20were%20detected.%20Each%20event%20was%20characterized%20by%20a%20tiny%20jet-like%20feature%20named%20%27nanojet%27%2C%20with%20lengths%20of%20%7E1500%20km%2C%20widths%20of%20%7E500%20km%20and%20durations%20of%2015%20s%20or%20less%2C%20perpendicular%20to%20the%20main%20flow%20of%20the%20plasma%20%28magnetic%20field%20direction%29%2C%20and%20with%20plane-of-the-sky%20and%20line-of-sight%20speeds%20up%20to%20200%20km%2Fs%20or%20more%20%28Fig.%202%29.%20The%20nanojets%20were%20best%20observed%20in%20the%20Si%20IV%201402%20%26Aring%3B%20spectral%20line%20%28and%20the%20SJI%201400%20%26Aring%3B%20channel%29%2C%20while%20there%20was%20almost%20%20no%20trace%20of%20the%20nanojets%20in%20the%20cooler%20Mg%20II%20k%20%28SJI%202796%20%26Aring%3B%29%20and%20Ca%20II%20H%20%28Hinode%2FSOT%2C%20observing%20simultaneously%29%20lines%2C%20indicating%20a%20very%20rapid%20heating%20process.%20The%20DEM%20and%20EUV%20absorption%20analysis%20provided%20temperatures%20and%20number%20densities%20estimates%20of%202%20-%205%20MK%20and%20%5Cbegin%7Bequation%7D%2010%5E%7B10%7D%20-%2010%5E%7B11%7D%20cm%5E%7B-3%7D%20%5Cend%7Bequation%7D%20for%20the%20nanojets%20respectively.%20The%20largest%20events%20were%20also%20accompanied%20with%20plasmoids%20ejected%20along%20the%20axis%20of%20the%20jets%20%28Fig.%201%29.%20Besides%20the%20perpendicular%20trajectory%20to%20the%20magnetic%20field%2C%20two%20other%20highly%20peculiar%20features%20were%20observed.%20First%2C%20the%20nanojets%20occurred%20both%20in%20clusters%20or%20in%20isolation%2C%20suggesting%20an%20impulsive%20and%20episodic%20process%20behind%20the%20jets.%20%20Second%2C%20the%20nanojets%20were%20almost%20all%20pointing%20inward%20with%20respect%20to%20the%20curvature%20of%20the%20loop%2C%20without%20any%20secondary%20jets%20pointing%20in%20the%20opposite%20direction%2C%20as%20expected%20from%20reconnection%20theory."},{"type":"image","file":"","url":"nuggetvideos/2021/04/21/pod_polito_vanessa_2021-04-21T16%3A35%3A18.398Z/SIIV-MgII-spectra-SJI.png","hash":"c320641c252ee35305858136ceed8b8b","mimeType":"image/png","caption":"Fig.%202.%20Spectra%20of%20nanojets.%20%28Top%20row%29%20A%20subset%20of%20the%20IRIS%20field-of-view%20in%20the%20SJI%202796%20%26Aring%3B%20%28left%29%20and%201400%20%26Aring%3B%20%28right%29%20channels%2C%20showing%20snapshots%20of%20two%20nanojets%20%28localized%20brightening%20events%20in%20the%20SJI%201400%20%26Aring%3B%20image%29.%20The%20IRIS%2FSG%20slit%20%28dashed%20line%29%20captures%20the%20spectra%20of%20the%20right-most%20nanojet.%20%28Bottom%20row%29%20The%20Mg%20II%20k%20%28left%29%20and%20Si%20IV%201402%20%26Aring%3B%20%28right%29%20spectra%20along%20the%20slit.%20The%20Si%20IV%20nanojet%20spectra%20overlaid%20over%20the%20image%20%28corresponding%20to%20the%20location%20indicated%20by%20the%20red%20line%29%20is%20characterized%20by%20enhanced%20intensity%20and%20a%20large%20blueshift%20%28up%20to%20100%20km%2Fs%20or%20more%29.%20A%20double-Gaussian%20fit%20to%20the%20spectra%20%28blue%20dashed%20curve%29%20reveals%20the%20strong%20blue%20shifted%20component."},{"type":"image","file":"","url":"nuggetvideos/2021/04/21/pod_polito_vanessa_2021-04-21T16%3A35%3A18.398Z/sketch-common_vs_nano.png","hash":"7c1b9421d55fd9f0e4404c2f96a588a4","mimeType":"image/png","caption":"Fig.%203.%20Nanojet%20interpretation.%20The%20nanojet%20is%20interpreted%20as%20the%20product%20of%20component%20magnetic%20reconnection%20%28small-angle%20reconnection%29%20due%20to%20the%20braiding%20and%20accumulated%20stress%20in%20the%20field%20lines.%20The%20localised%20heating%20combined%20with%20the%20fast%20sideways%20advection%20of%20the%20reconnected%20field%20lines%20from%20magnetic%20tension%20produces%20the%20nanojets."},{"type":"text","text":"The%20nanojets%20are%20interpreted%20as%20the%20signature%20of%20magnetic%20reconnection%20at%20small%20angles%20%28component%20reconnection%29.%20In%20this%20scenario%2C%20the%20nanojet%20is%20the%20result%20of%20the%20sideways%20advection%20of%20the%20magnetic%20field%20lines%2C%20driven%20by%20magnetic%20tension%20and%20pushing%20the%20heated%20plasma%20sideways%20at%20Alfv%26eacute%3Bnic%20speeds%20%28Fig.%203%29.%20The%20nanojet%20is%20therefore%20different%20from%20the%20usual%20reconnection%20jets%20%28such%20as%20chromospheric%20jets%29%20in%20the%20sense%20that%20the%20fastest%20flows%20are%20not%20field-aligned%20and%20reflect%20the%20fast%20reconfiguration%20of%20the%20magnetic%20field%20lines%20post-reconnection.%20This%20interpretation%20is%20supported%20by%203D%20MHD%20numerical%20simulations%20with%20the%20PLUTO%20code%2C%20that%20reproduced%20the%20thermal%20and%20dynamic%20properties%20of%20the%20jets.%20We%20speculate%20that%20the%20peculiar%20unidirectional%20feature%20is%20a%20product%20of%20global%20loop%20curvature%20and%2For%20the%20local%20curvature%20due%20to%20braiding%2C%20leading%20to%20asymmetry%20in%20the%20evolution%20of%20the%20magnetic%20tension%20force%20at%20either%20side%20of%20the%20reconnection%20region."},{"type":"image","file":"","url":"nuggetvideos/2021/04/21/pod_polito_vanessa_2021-04-21T16%3A35%3A18.398Z/hotloop.png","hash":"f0931e86cfb2ac000d8beb070b0a4b23","mimeType":"image/png","caption":"Fig.%204.%20A%20coronal%20loop%20forms.%20Following%20the%20nanojet%20occurrence%20%28roughly%20150%20events%20in%2013%20min%29%2C%20the%20initially%20cool%20loop%20heats%20up%20to%20millions%20of%20degrees%2C%20captured%20in%20various%20AIA%20and%20IRIS%20channels.%20From%20left%20to%20right%3A%20IRIS%201400%20%26Aring%3B%20%2860%2C000%20K%29%2C%20AIA%20304%20%26Aring%3B%20%28100%2C000%20K%29%2C%20AIA%20171%20%26Aring%3B%20%28800%2C000%20K%29%20and%20AIA%20193%20%26Aring%3B%20%281%2C500%2C000%20K%29%20images."},{"type":"text","text":"Globally%2C%20the%20nanojets%20were%20observed%20to%20spread%20across%20and%20along%20the%20loop%20in%20an%20avalanche-like%20progression%20%28%7E150%20events%20over%2013%20min%29.%20Following%20the%20nanojets%2C%20hot%20coronal%20strands%20formed%20starting%20from%20the%20nanojet%20locations%2C%20spanning%20the%20entire%20length%20of%20the%20loop%20%28Fig.%204%29.%20The%20initial%20coronal%20rain%20along%20the%20cool%20structure%2C%20here%20acting%20as%20a%20high-resolution%20tracer%20of%20the%20magnetic%20field%20dynamics%2C%20revealed%20misalignments%20between%20the%20strands%20of%20up%20to%2025%20degrees%2C%20suggestive%20of%20braiding.%20During%20the%20heating%20episodes%20the%20amount%20of%20apparent%20braiding%20and%20misalignment%20was%20reduced%2C%20accompanied%20with%20complex%20internal%20rotations%20and%20signatures%20of%20untwisting%2C%20thereby%20matching%20the%20reconnection%20picture.%20The%20driver%20of%20the%20reconnection%20was%20suspected%20to%20be%20the%20prominence%20at%20the%20apex%20of%20the%20loop%2C%20which%20gave%20indications%20of%20becoming%20partly%20unstable%20through%20the%20unloading%20material%20%28similar%20to%20the%20scenario%20suggested%20in%20Keppens%20%26amp%3B%20Xia%202014%29.%20The%20magnetic%20field%20lines%20released%20from%20the%20material%20would%20expand%20from%20below%2C%20putting%20pressure%20on%20the%20loop%20structure%20above%2C%20anchored%20to%20the%20prominence.%20It%20was%20hypothesised%20that%20such%20nanojets%20should%20be%20independent%20of%20the%20reconnection%20driver%20and%20should%20therefore%20be%20observed%20in%20various%20coronal%20structures%20subject%20to%20braiding."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2021NatAs...5...54A/abstract\">Antolin, P., Pagano, P., Testa, P., Petralia, A., Reale, F., Nat. Astron. 5, 54 (2021) </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2008ApJ...688..669A/abstract\"> Antolin, P., et al. ApJ, 688, 669 (2008)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014ApJ...789...22K/abstract\"> Keppens, R. & Xia, C. ApJ 789, 22 (2014)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1988ApJ...330..474P/abstract\">Parker, E. N., ApJ 330, 474 (1988)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2013ApJ...770L...1T/abstract\"> Testa, P. et al. ApJL 770, L1 (2013)</a>","","","","",""],"pubDate":"2021-05-11T22:43:11.902Z"}]