IRIS Nugget
Welcome to the IRIS Science Nuggets: highlights of recent IRIS scientific results for the solar physics community.
{"id":"pod_polito_vanessa_2021-06-10T18:56:55.307Z","submitter":"(1) Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA, 94035, USA; (2) Lockheed Martin Solar and Astrophysics Laboratory, Building 252, 3251 Hanover Street, Palo Alto, CA, 94304, USA","author":"Magnus Woods (1,2)","status":"published","creation-date":"2021-06-10T18:56:55.312Z","last-modified-date":"2021-08-10T20:25:13.776Z","credit":"Alberto Sainz Dalda(1,2), Bart De Pontieu(2)","title":"Unsupervised Machine Learning for the Identification of Pre-flare Spectroscopic Signatures","contentBlocks":[{"type":"text","text":"In%20this%20study%20we%20use%20the%20unsupervised%20machine%20learning%20technique%20k-means%20clustering%20upon%20high%20resolution%20spectroscopic%20observations%20of%20the%20Mg%20II%20lines%20made%20by%20the%20Interface%20Region%20Imaging%20Spectrometer%20%28IRIS%2C%20De%20Pontieu%20et%20al.%202014%29%20to%20try%20and%20identify%20pre-flare%20signatures%20in%20order%20to%20help%20elucidate%20the%20physical%20mechanisms%20behind%20flaring.%20%0A%0AThe%20k-means%20clustering%20algorithm%20%28MacQueen%20et%20al.%201967%29%20is%20widely%20used%20to%20categorise%20many%20types%20of%20data.%20We%20employed%20it%20to%20distinguish%20between%20spectra%20that%20occur%20widely%20in%20pre-flare%2C%20quiescent%20active%20region%20and%20quiet%20sun%20rasters%2C%20and%20those%20that%20appear%20in%20the%20pre-flare%20data%20sets%20only.%20%20We%20chose%20data%20from%208%20solar%20flares%20of%20X%20and%20M%20class%2C%20and%20selected%209%20rasters%20from%20each%20data%20set%2C%20starting%2040%20minutes%20prior%20to%20flaring%20in%205%20minute%20increments%20until%20flare%20onset%20as%20defined%20by%20the%20GOES%20flarelist.%20These%20data%20at%20each%20time%20step%20were%20then%20clustered%20alongside%20a%20large%20data%20set%20made%20up%20of%2032%20Quiescent%20AR%20data%20sets%20and%206%20Quiet%20Sun%20data%20sets.%20%0A%0AFigure%201%20shows%20the%20types%20of%20spectra%20that%20our%20clustering%20found%20only%20to%20occur%20in%20the%20pre-flare%20data%20sets.%20%20We%20can%20see%20that%20these%20eight%20broad%20categories%20are%20profiles%20which%20exhibit%3A%20%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines%3B%20double%20peaked%20k%20%26amp%3B%20h%20lines%2C%20with%20emission%20in%20the%20Mg%20II%20triplet%20line%3B%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%3B%20double%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%3B%20Broad%20Shouldered%20Mg%20II%20k%20%26amp%3B%20h%3B%20Broad%20Mg%20II%20k%20%26amp%3B%20h%3B%20Cosmic%20Ray%20hits%3B%20and%20the%20final%20group%20is%20of%20clusters%20which%20are%20irregular%20profiles%20with%20broad%20wings.%20%20Of%20these%208%20types%20of%20preflare%20cluster%2C%20the%20most%20common%20is%20spectra%20showing%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines.%20Profiles%20of%20this%20type%20comprise%20and%20average%20of%2076%25%20of%20all%20the%20identified%20preflare%20spectra%20at%20each%20timestep."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/clster_examples_v2.jpg","hash":"6ed0a249d9a67657ef997bc23dc7c20c","mimeType":"image/jpeg","caption":"Figure%201%3A%20This%20figure%20shows%20examples%20of%20the%208%20categories%20of%20pre-flare%20Representative%20Profiles.%20As%20before%2C%20the%20representative%20profile%20is%20shown%20in%20orange%2C%20with%20the%20black%20corresponding%20to%20the%20individual%20profiles%20that%20contribute%20to%20it."},{"type":"text","text":"The%20location%20of%20the%20pre-flare%20clusters%20was%20also%20investigated%2C%20as%20an%20example%20of%20this%20for%20one%20flare%20Figure%202%20shows%20the%20locations%20of%20all%20pre-flare%20clusters%20found%20at%20each%20time%20step%20overlayed%20onto%20the%20IRIS%20slit-jaw%20images.%20What%20we%20see%20when%20examining%20the%20locations%20of%20all%20the%20preflare%20clusters%20is%20that%20they%20predominately%20occur%20in%20regions%20where%20the%20flare%20ribbons%20will%20occur%20during%20the%20flare%20%28ribbon%20locations%20at%20flare%20peak%20are%20shown%20by%20the%20black%20contours%20in%20Figure%202%2C%20and%20by%20the%20green%20contours%20in%20Figure%203%29%20or%20are%20related%20with%20transient%20brightenings%20within%20the%20center%20of%20the%20active%20regions.%20Figure%203%2C%20for%20the%20same%20times%20and%20fields%20of%20view%2C%20shows%20the%20pre-flare%20clusters%20overlayed%20upon%20the%20corresponding%20SDO%20HMI%20line-of-sight%20magnetograms.%20From%20these%20we%20find%20that%20the%20majority%20of%20the%20pre-flare%20clusters%20broadly%20align%20with%20regions%20of%20intersection%20between%20the%20positive%20and%20negative%20magnetic%20field%20%28the%20white%20and%20black%20areas%20in%20the%20images%20respectively%29."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/dataset_3_locations.jpg","hash":"98e7c46274bdaccaea0f5e86d89ee81","mimeType":"image/jpeg","caption":"Figure%202%3A%20In%20this%20figure%20we%20see%20the%20locations%20of%20the%20pre-flares%20clusters%20found%20prior%20to%20the%20X2.1%20flare%20SOL2015-03-11T16%3A22%20at%20each%20of%20the%20nine%20time%20steps%20clustered.%20For%20each%20time%20step%20the%20corresponding%20IRIS%20SJI%20image%20is%20shown%2C%20with%20the%20location%20of%20the%20raster%20slit%20positions%20shown%20as%20the%20dotted%20lines.%20The%20location%20of%20the%20spectra%20in%20each%20individual%20cluster%20are%20shown%20in%20a%20unique%20colour%2C%20which%20are%20detailed%20by%20the%20neighbouring%20colour%20bar%20for%20each%20time%20step.%20The%20location%20of%20the%20flare%20ribbons%2C%20determined%20at%20the%20peak%20time%20of%20the%20flare%20are%20shown%20overlayed%20as%20black%20contours."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/dataset_3_locations_hmi_continuum.png","hash":"d45a389cf98a805073cb402ab8332466","mimeType":"image/png","caption":"Figure%203%3A%20In%20this%20figure%20we%20see%20the%20locations%20of%20the%20pre-flares%20clusters%20found%20prior%20to%20the%202015-03-11%20X2.1%20flare%20at%20each%20of%20the%20nine%20time%20steps%20clustered.%20For%20each%20time%20step%20the%20corresponding%20SDO%20HMI%20image%20is%20shown%2C%20with%20the%20location%20of%20the%20raster%20slit%20positions%20shown%20as%20the%20dotted%20lines.%20The%20location%20of%20the%20spectra%20in%20each%20individual%20cluster%20are%20shown%20in%20a%20unique%20colour%2C%20which%20are%20detailed%20by%20the%20neighbouring%20colour%20bar%20for%20each%20time%20step.%20The%20location%20of%20the%20flare%20ribbons%2C%20determined%20at%20the%20peak%20time%20of%20the%20flare%20are%20shown%20overlayed%20as%20green%20contours.%20Also%20overlain%20as%20contours%20are%20the%20locations%20of%20the%20penumbra%20%28purple%29%20and%20umbra%20%28grey%29."},{"type":"text","text":"We%20then%20decided%20to%20further%20investigate%20the%20conditions%20that%20could%20have%20produced%20the%20spectra%20showing%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines.%20From%20existing%20studies%20modelling%20Mg%20II%20profiles%20have%20found%20that%20in%20plage%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%20can%20be%20produced%20in%20a%20hot%2C%20dense%20chromosphere%2C%20with%20temperatures%20around%206500K%20%28Carlsson%20et%20al.%202015%29%2C%20while%20another%20study%20conducted%20under%20flaring%20conditions%20found%20that%20increased%20temperatures%2C%20densities%2C%20or%20velocities%20in%20the%20upper%20chromosphere%20can%20produce%20the%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%20%28Rubio%20da%20Costa%20et%20al.%202017%29.%20Recent%201D%20RHD%20modelling%20of%20these%20lines%20by%20Zhu%20et%20al.%20%282019%29%20also%20found%20that%20increased%20electron%20density%20in%20the%20upper%20chromosphere%20could%20produce%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20profiles.%20Additionally%2C%20this%20work%20found%20that%20these%20increased%20electron%20densities%20could%20result%20in%20profiles%20with%20single%20peaked%20%20Mg%20II%20UV%20triplet%20lines%2C%20while%20Pereira%20et%20al.%20%282015%29%20found%20that%20temperature%20increases%20in%20the%20upper%20chromosphere%20could%20produce%20these%20single%20peaked%20triplet%20lines.%20%0AWe%20conducted%20simultaneous%20inversions%20of%20the%20Mg%20II%20k%20%26amp%3B%20h%20lines%20and%20the%20C%20II%201334%20and%201335%20lines%20following%20the%20method%20of%20Sainz%20Dalda%202021%20in%20order%20to%20accurately%20investigate%20the%20thermodynamic%20conditions%20that%20produced%20these%20spectra.%20Figure%204%20shows%20the%20results%20of%20a%20typical%20spectra%20of%20this%20type%20that%20was%20inverted.%20We%20find%20that%20the%20model%20atmospheres%20of%20theses%20profiles%20show%20increases%20in%20both%20temperature%20and%20electron%20density%20in%20the%20chromosphere.%20This%20would%20seem%20to%20agree%20with%20the%20existing%20results%20above."},{"type":"image","file":"","url":"nuggetvideos/2021/06/10/pod_polito_vanessa_2021-06-10T18%3A56%3A55.307Z/nugget_inversion.png","hash":"5a030ef78d9e44fee5e95d176a0b6dae","mimeType":"image/png","caption":"Figure%204.%20This%20figure%20shows%20the%20input%20spectra%2C%20inversion%20fit%2C%20and%20resultant%20model%20atmospheres%20for%20a%20single%20peaked%20pre-flare%20Mg%20II%20spectrum.%20In%20each%20panel%20the%20upper%20and%20middle%20images%20show%20the%20observed%20C%20II%20and%20Mg%20II%20spectra%20%28purple%29%20respectively%20with%20the%20model%20fits%20overlaid%20%28black%29.%20The%20Mg%20II%20images%20also%20has%20a%20synthetic%20profile%20produced%20from%20the%20FALC%20model%20%28dashed-blue%29%20overlain.%20Two%20double-axes%20below%20show%20the%20parameters%20of%20the%20resultant%20model%20from%20the%20inversion%20of%20the%20observed%20profiles%20%28solid%20lines%29%20and%20for%20the%20FALC%20model%20%28dashed%20line%29%20used%20as%20the%20initial%20guess%20model%20in%20the%201st%20cycle%20of%20the%20inversion.%20The%20temperature%20and%20electron%20%28orange%20and%20blue%20respectively%29%20density%20are%20shown%20on%20the%20left%2C%20while%20microturbulence%20%28vturb%29%20and%20line-of-sight%20velocity%20%28vLOS%29%20are%20shown%20on%20the%20right%20%28purple%20and%20green%20respectively%29."},{"type":"text","text":"From%20both%20our%20inversions%20and%20observation%20results%2C%20we%20conclude%20that%20these%20pre-flare%20spectra%20which%20exhibit%20single%20peaked%20Mg%20II%20k%20%26amp%3B%20h%20lines%2C%20with%20single%20peaked%20emission%20in%20the%20Mg%20II%20UV%20triplet%20lines%20are%20often%20seen%20up%20to%2040%20minutes%20prior%20to%20flaring%20and%20that%20these%20spectra%20are%20most%20likely%20produced%20during%20small%20scale%20heating%20events%20in%20the%20chromosphere."}],"references":["<a href=\"https://link.springer.com/article/10.1007/s11207-014-0485-y\">De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Solar Physics, 289, 2733 </a>","<a href=\"https://projecteuclid.org/ebooks/berkeley-symposium-on-mathematical-statistics-and-probability/Proceedings%20of%20the%20Fifth%20Berkeley%20Symposium%20on%20Mathematical%20Statistics%20and%20Probability,%20Volume%201:%20Statistics/chapter/Some%20methods%20for%20classification%20and%20analysis%20of%20multivariate%20observations/bsmsp/1200512992\">MacQueen J., et al. 1967, in Proceedings of the fifth Berkeley symposium on mathematical statistics and probability, Oakland, CA, USA </a>","<a href=\"https://iopscience.iop.org/article/10.1088/2041-8205/809/2/L30\">Carlsson, M., Leenaarts, J., & De Pontieu, B. 2015, ApJL, 809, L30 </a>","<a href=\"https://iopscience.iop.org/article/10.3847/1538-4357/aa6eaf\">Rubio da Costa, F., & Kleint, L. 2017, ApJ, 842, 82 </a>","<a href=\"https://iopscience.iop.org/article/10.3847/1538-4357/ab2238\">Zhu, Y., Kowalski, A. F., Tian, H., et al. 2019, The Astrophysical Journal, 879, 19 </a>","<a href=\"https://iopscience.iop.org/article/10.1088/0004-637X/806/1/14\">Pereira, T. M. D., Carlsson, M., De Pontieu, B., & Hansteen, V. 2015, ApJ, 806, 14 </a>","Sainz Dalda, A. in prep.","","",""],"pubDate":"2021-08-10T20:25:18.54Z"}