IRIS Nugget
Welcome to the IRIS Science Nuggets: highlights of recent IRIS scientific results for the solar physics community.
{"id":"pod_polito_vanessa_2021-11-22T17:44:45.468Z","submitter":"Daniel Nobrega-Siverio (dnobrega@iac.es)","author":"Daniel Nobrega-Siverio [1,2,3,4], Salvo Guglielmino [5,6], Alberto Sainz Dalda [7,8,9]","status":"published","creation-date":"2021-11-22T17:44:45.471Z","last-modified-date":"2021-12-08T20:28:20.391Z","credit":"[1] Instituto de Astrofisica de Canarias. [2] Universidad de La Laguna. [3] Rosseland Centre for Solar Physics. [4] Institute of Theoretical Astrophysics. [5] Dipartimento di Fisica e Astronomia - Ettore Majorana. [6] INAF - Osservatorio Astrofisico di Catania. [7] Lockheed Martin Solar and Astrophysics Laboratory. [8] Bay Area Environmental Research Institute. [9] Stanford University.","title":"Solar surges related to UV bursts: Characterization through k-means, inversions, and density diagnostics.","contentBlocks":[{"type":"text","text":"Surges%20are%20key%20chromospheric%20ejections%20closely%20related%20to%20other%20solar%20phenomena%20such%20as%20UV%20bursts%20and%20coronal%20jets.%20Even%20though%20surges%20have%20been%20observed%20for%20decades%20now%2C%20questions%20regarding%20their%20fundamental%20physical%20properties%20such%20as%20temperature%20and%20density%2C%20as%20well%20as%20their%20impact%20on%20upper%20layers%20of%20the%20solar%20atmosphere%20remain%20open.%20In%20this%20study%20%28Nobrega-Siverio%20et%20al.%202021%29%2C%20we%20address%20the%20current%20lack%20of%20inverted%20models%20and%20diagnostics%20of%20surges%2C%20characterizing%20the%20chromospheric%20and%20transition%20region%20plasma%20of%20these%20phenomena.%20To%20that%20end%2C%20we%20have%20analyzed%20an%20episode%20of%20recurrent%20surges%20related%20to%20UV%20bursts%20observed%20in%20April%202016%20with%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%2C%20focusing%20on%20the%20near-%20and%20far-UV%20spectra%20obtained%20through%20dense%2064-step%20raster%20scans%20%28see%20also%20Guglielmino%20et%20al.%202019%29.%0A%0ALeft%20column%20of%20Figure%201%20shows%20radiance%20maps%20of%20Mg%20II%20k%202796.3%20%26Aring%3B%20for%20the%20four%20rasters%20studied%2C%20where%20the%20surges%20are%20clearly%20distinguishable%20as%20dark%20structures%20delimited%20by%20a%20solid%20contour.%20To%20analyze%20the%20Mg%20II%20h%26amp%3Bk%20spectra%2C%20we%20have%20used%20k-means%3A%20a%20machine%20learning%20technique%20that%20can%20be%20used%20to%20classify%20a%20set%20of%20profiles%20in%20k%20disjoint%20clusters%20%28or%20groups%29%20based%20on%20the%20similarity%20of%20the%20profiles%20%28see%20the%20Scikit-learn%20Python%20tools%20by%20Pedregosa%20et%20al.%202011%29.%20By%20doing%20this%2C%20we%20can%20obtain%20Mg%20II%20h%26amp%3Bk%20representative%20profiles%20from%20the%20observations%2C%20also%20reducing%20the%20number%20of%20profiles%20to%20invert.%20The%20second%20column%20of%20Figure%201%20contains%20the%20distribution%20of%20the%20160%20clusters%20per%20raster%20obtained%20with%20the%20k-means.%20By%20ordering%20the%20clusters%20depending%20on%20their%20number%20of%20profiles%2C%20we%20can%20already%20discern%20that%20surges%20and%20their%20surroundings%20have%20clearly%20different%20Mg%20II%20h%26amp%3Bk%20profiles%20from%20other%20regions."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_02 (3).png","hash":"83df248a9a1c4377edcb4180978d5046","mimeType":"image/png","caption":"Figure%201.%20Observed%20surges%20and%20results%20from%20k-means%20and%20inversions.%20Columns%20from%20left%20to%20right%3A%20radiance%20maps%20in%20the%20core%20of%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20line%3B%20cluster%20labels%20from%20the%20k-means%20ordered%20by%20the%20amount%20of%20profiles%20within%20a%20cluster%3B%20and%20maps%20at%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-5.2%20for%20temperature%2C%20T%2C%20electron%20number%20density%2C%20%5Cbegin%7Bequation%7Dn_e%2C%5Cend%7Bequation%7D%20and%20line-of-sight%20velocity%2C%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%2C%20from%20the%20inversions%20of%20the%20Mg%20II%20h%26amp%3Bk%20line%20using%20the%20STiC%20code.%20Black%20contours%20delimit%20the%20bulk%20of%20the%20surges%20visible%20in%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20radiance%20maps."},{"type":"text","text":"Once%20we%20obtain%20the%20representative%20Mg%20II%20h%26amp%3Bk%20profiles%20from%20the%20k-means%2C%20we%20invert%20them%20using%20the%20state-of-the-art%20STiC%20code%20%28de%20la%20Cruz%20Rodriguez%20et%20al.%202019%29.%20The%20three%20rightmost%20columns%20of%20Figure%201%20show%20the%20results%20from%20the%20inversions%20for%20temperature%2C%20electron%20number%20density%20and%20line-of-sight%20velocity%20at%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%3D-5.2.%20In%20the%20maps%2C%20it%20is%20possible%20to%20perceive%20that%20the%20surges%20have%20some%20peculiarities%20in%20their%20physical%20properties%2C%20for%20example%2C%20they%20are%20mostly%20cooler%20and%20with%20a%20smaller%20electron%20number%20density%20%20than%20their%20surroundings.%20To%20get%20a%20whole%20perspective%20of%20these%20properties%2C%20we%20have%20performed%20a%20statistical%20analysis%20within%20the%20contour%20that%20delimits%20the%20different%20surges%20in%20Figure%201.%20The%20results%20are%20shown%20in%20Figure%202%2C%20through%20histograms%20for%20the%20three%20above-mentioned%20physical%20quantities.%20To%20create%20these%20histograms%2C%20we%20considered%20the%20range%20of%20optical%20depths%20in%20which%20the%20uncertainties%20are%20smaller%20for%20each%20physical%20quantity."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_04 (2).png","hash":"45a020217fce224a83b3590e3ac3a213","mimeType":"image/png","caption":"Figure%202.%20Statistical%20results%20for%20T%2C%20%5Cbegin%7Bequation%7Dn_e%5Cend%7Bequation%7D%2C%20and%20%5Cbegin%7Bequation%7Dv_%7Blos%7D%5Cend%7Bequation%7D%20obtained%20within%20the%20contour%20that%20delimits%20the%20different%20surges%20in%20Figure%201.%20The%20statistics%20contain%20data%20from%20the%20optical%20depths%20where%20inversions%20are%20more%20reliable%2C%20from%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-6.0%20to%20-3.2%2C%20for%20the%20temperature%2C%20and%20from%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%20%3D%20-6.0%20to%20-4.8%20for%20the%20density%20and%20velocity.%20Histograms%20are%20stacked%20by%20rasters%2C%20showing%20that%20the%20different%20surges%20have%20similar%20properties%2C%20and%20by%20log%28%5Cbegin%7Bequation%7D%5Ctau%5Cend%7Bequation%7D%29%2C%20illustrating%20the%20variation%20of%20the%20physical%20parameters%20with%20the%20optical%20depth."},{"type":"text","text":"From%20the%20histograms%2C%20we%20conclude%20that%20the%20surges%20have%20their%20most%20probable%20temperature%20around%206000%20K%2C%20electronic%20number%20densities%20mostly%20concentrated%20from%20%5Cbegin%7Bequation%7D1.6%5Ctimes10%5E%7B11%7D%5Cend%7Bequation%7D%20to%20%5Cbegin%7Bequation%7D10%5E%7B12%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%2C%20and%20velocities%20of%20a%20few%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B-1%7D%5Cend%7Bequation%7D.%20In%20addition%2C%20we%20have%20shown%20that%20the%20statistical%20distributions%20of%20these%20properties%20are%20very%20similar%20for%20the%20different%20surges%2C%20meaning%20that%20these%20ejections%20can%20be%20well%20constrained%20in%20terms%20of%20their%20physical%20quantities.%0A%0A%0AWe%20have%20also%20studied%20the%20transition%20region%20of%20surges%20through%20the%20far-UV%20spectra%2C%20being%20able%20to%20find%20for%20the%20first%20time%20detectable%20emission%20in%20both%20the%20O%20IV%201399.8%20%26Aring%3B%20and%201401.2%20%26Aring%3B%20lines%20related%20to%20surges.%20This%20finding%20is%20relevant%20because%20it%20clearly%20demonstrates%20that%20surges%20have%20a%20transition%20region%20counterpart%20even%20in%20the%20weakest%20far-UV%20lines%2C%20as%20well%20as%20it%20gives%20observational%20support%20to%20the%20theoretical%20predictions%20by%20Nobrega-Siverio%20et%20al.%202018.%20Figure%203%20contains%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20radiance%20map%20together%20with%20O%20IV%20radiance%20maps%20at%20different%20positions%2C%20showing%20that%20the%20location%20of%20the%20brightest%20O%20IV%20regions%20can%20be%20found%20within%20the%20bulk%20of%20the%20surges%20and%2For%20in%20their%20boundaries%20following%20the%20threads%20of%20the%20surges.%20This%20is%20particularly%20evident%20in%20the%20third%20and%20fourth%20rasters."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_05.png","hash":"2f17503f528a55da88dab6b628b966f1","mimeType":"image/png","caption":"Figure%203.%20Radiance%20maps%20showing%20the%20O%20IV%20emissivity%20of%20the%20surges.%20From%20left%20to%20right%3A%20Radiance%20maps%20in%20the%20core%20of%20the%20Mg%20II%20k%202796.3%20%26Aring%3B%20line%20%28first%20column%29%3B%20in%20the%20core%20of%20the%20O%20IV%201401.2%20%26Aring%3B%20line%20%28second%20column%29%3B%20in%20the%20blue%20and%20red%20wings%20at%20-50%20and%200%20%5Cbegin%7Bequation%7Dkm%7Es%5E%7B-1%7D%5Cend%7Bequation%7D%20of%20O%20IV%201401.2%20%26Aring%3B%20%28third%20and%20fourth%20columns%2C%20respectively%29%3B%20and%20composite%20image%20of%20the%20blue%20and%20red%20wing%20radiance%20maps%20%28fifth%20column%29.%20Equivalent%20maps%20are%20plotted%20for%20the%20O%20IV%201399.8%20%26Aring%3B%20line%20%28sixth%20to%20ninth%20columns%29.%20The%20contours%20are%20the%20same%20as%20in%20Figure%201."},{"type":"text","text":"The%20simultaneous%20finding%20of%20O%20IV%201399.8%20%26Aring%3B%20and%201401.2%20%26Aring%3B%20allowed%20us%20to%20estimate%20the%20electron%20density%20in%20the%20transition%20region%20of%20the%20surges.%20Applying%20density%20diagnostics%20%28see%2C%20e.g.%2C%20Polito%20et%20al.%202016%29%2C%20we%20obtained%20a%20electron%20number%20density%20in%20the%20range%20of%20%5Cbegin%7Bequation%7D2.5%5Ctimes10%5E%7B10%7D%20-10%5E%7B12%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%20for%20the%20surge%20layers%20emitting%20in%20the%20far-UV.%0A%0AIn%20this%20work%2C%20we%20have%20also%20qualitatively%20compared%20the%20observations%20with%20three%20surge%20numerical%20experiments%20%28Nobrega-Siverio%20et%20al.%202016%2C%202017%2C%202018%29%20performed%20with%20the%20Bifrost%20code%20%28Gudiksen%20et%20al.%202011%29.%20Figure%204%20shows%20the%20electron%20number%20density%20for%20these%20three%20simulations%2C%20with%20superimposed%20contours%20at%20different%20temperatures%20that%20highlight%20the%20multi-thermal%20structure%20of%20these%20ejections.%20We%20have%20found%20similarities%20in%20terms%20of%20the%20topology%20that%20may%20also%20explain%20the%20location%20of%20the%20observed%20brightest%20O%20IV%20regions%20with%20respect%20to%20the%20bulk%20of%20the%20surges.%20In%20addition%2C%20the%20core%20of%20the%20simulated%20surges%20is%20quite%20concentrated%20around%206000%20K%2C%20which%20agrees%20with%20the%20values%20from%20the%20inversions%20we%20have%20found%20here."},{"type":"image","file":"","url":"nuggetvideos/2021/11/22/pod_polito_vanessa_2021-11-22T17%3A44%3A45.468Z/figure_07 (1).png","hash":"4b96f8b3619623126bd457fe9f5fc75b","mimeType":"image/png","caption":"Figure%204.%20Electron%20number%20density%20for%20three%20different%20simulated%20surges.%20Contours%20of%20temperature%20are%20superimposed%20for%20T%3D6%20kK%20%28green%29%2C%20T%3D10%20kK%20%28blue%29%2C%20and%20T%3D200%20kK%20%28red%29.%20Panel%20A%3A%20Surge%20from%20Nobrega-Siverio%20et%20al.%202016.%20Panels%20B%20and%20C%3A%20Surges%20from%20Nobrega-Siverio%20et%20al.%202017%2C%202018."},{"type":"text","text":"The%20combination%20of%20methods%20and%20results%20obtained%20in%20this%20work%20opens%20new%20possibilities%20for%20the%20analysis%20and%20diagnostics%20of%20surges%2C%20and%20an%20ISSI%20team%20devoted%20to%20unravel%20the%20surges%20is%20currently%20exploring%20them%20%28see%20https%3A%2F%2Fteams.issibern.ch%2Funravelingsurges%2F%20for%20further%20details%29."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2021A%26A...655A..28N/abstract\"> Nobrega-Siverio, D., Guglielmino, S. L., & Sainz Dalda, A. 2021, A&A, 655, A28 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2014SoPh..289.2733D/abstract\"> De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Sol. Phys., 289, 2733</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019ApJ...871...82G/abstract\"> Guglielmino, S. L., Young, P. R., & Zuccarello, F. 2019, ApJ, 871, 82 </a>","<a href=\"https://www.jmlr.org/papers/volume12/pedregosa11a/pedregosa11a.pdf\"> Pedregosa, F., Varoquaux, G., Gramfort, A., et al. 2011, J. Mach. Learn. Res., 12, 2825 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2019A%26A...623A..74D/abstract\"> de la Cruz Rodriguez, J., Leenaarts, J., Danilovic, S., & Uitenbroek, H. 2019, A&A, 623, A74 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016A%26A...594A..64P/abstract\"> Polito, V., Del Zanna, G., Dudik, J., et al. 2016a, A&A, 594, A64 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2018ApJ...858....8N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., & Martinez-Sykora, J. 2018, ApJ, 858, 8 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2011A%26A...531A.154G/abstract\"> Gudiksen, B. V., Carlsson, M., Hansteen, V. H., et al. 2011, A&A, 531, A154 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2016ApJ...822...18N/abstract\"> Nobrega-Siverio, D., Moreno-Insertis, F., & Martinez-Sykora, J. 2016, ApJ, 822, 18 </a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...850..153N/abstract\"> Nobrega-Siverio, D., Martinez-Sykora, J., & Moreno-Insertis, F. & Rouppe van der Voort. L. 2017, ApJ, 850, 153 </a>"],"pubDate":"2021-12-09T20:35:14.976Z"}