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.

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[{"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 &amp; 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., &amp; 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., &amp; 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., &amp; 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_2022-05-26T17:47:04.706Z","submitter":"Andrew Hillier","author":"Andrew Hillier[1] &amp; 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 &amp; 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., &amp; Watanabe, H. 2011, PASJ, 63, 19</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...864L..10H/abstract\">Hillier, A., &amp; Polito, V. 2018, ApJ, 864, L10</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...651A..60H/abstract\">Hillier, A., &amp; Polito, V. 2021, A&amp;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 &amp; 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&amp;A 55, 305 (1977)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...654A..51B/abstract\">Bose, Souvik et al., A&amp;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&amp;A 647, 147 (2021a)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017Sci...356.1269M/abstract\">Mart&Atilde;&shy;nez-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%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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&amp;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&amp;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&amp;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 &amp; 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 &amp; 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 &amp; 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=\"&acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;€&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;œhttps://ui.adsabs.harvard.edu/abs/2018ApJ...856..178P/abstract&quot;\"> Polito et al., ApJ, 856, 178 (2018)</a>","<a href=\"&acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;€&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;œhttps://ui.adsabs.harvard.edu/abs/1997LNP...489..159C/abstract&quot;\"> Carlsson &amp; Stein LNP, 489, 159, (1997)</a>","<a href=\"&acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;€&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;œhttps://ui.adsabs.harvard.edu/abs/2005ApJ...630..573A/abstract&quot;\"> Allred et al., ApJ, 630, 573 (2005)</a>","<a href=\"&acirc;&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;€&Acirc;&Acirc;&Acirc;&Acirc;&Acirc;œhttps://ui.adsabs.harvard.edu/abs/2015ApJ...809..104A/abstract&quot;\"> 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., &amp; Sainz Dalda, A. 2021, A&amp;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., &amp; 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., &amp; Uitenbroek, H. 2019, A&amp;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&amp;A, 594, A64 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...858....8N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., &amp; 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&amp;A, 531, A154 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...822...18N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., &amp; 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., &amp; Moreno-Insertis, F. &amp; 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., &amp; 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., &amp; 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., &amp; 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., &amp; Petterson, B. 2003a, in Innovative Telescopes and Instrumentation for Solar Astrophysics, eds. S. L. Keil, &amp; 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., Sim&Atilde;&micro;es P. J. A., Qiu J., Fletcher L., A&amp;A, 582, A50 (2015)","Leenaarts J., Pereira T. M. D., Carlsson M., Uitenbroek H., De Pontieu B., ApJ, 772, 90 (2013)","N&Atilde;&sup3;brega-Siverio D., Mart&Atilde;&shy;nez-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&amp;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 &amp; 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., &amp; De Pontieu, B. 2015, ApJL, 809, L30 </a>","<a href=\"https://iopscience.iop.org/article/10.3847/1538-4357/aa6eaf\">Rubio da Costa, F., &amp; 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., &amp; 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 &amp; 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&amp;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&amp;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&amp;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&amp;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., &amp; 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. &amp; 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"}]