{"id":"pod_polito_vanessa_2023-08-25T21:28:28.536Z","submitter":"Yan Xu","author":"Yan Xu [1,2], Graham S. Kerr [3,4], Vanessa Polito [5,6], Nengyi Huang [1,2], Ju Jing [1,2] and Haimin Wang [1,2]","status":"published","creation-date":"2023-08-25T21:28:28.539Z","last-modified-date":"2023-09-13T01:04:43.507Z","credit":"1. Institute for Space Weather Sciences, New Jersey Institute of Technology 2. Big Bear Solar Observatory, New Jersey Institute of Technology 3. NASA Goddard Space Flight Center, Heliophysics Science Division 4. Department of Physics, Catholic University of America 5. Bay Area Environmental Research Institute 6. Lockheed Martin Solar and Astrophysics Laboratory","title":"Extreme Red-wing Enhancements of UV Lines During the 2022 March 30 X1.3 Solar Flare","contentBlocks":[{"type":"text","text":"Flare%20heating%20in%20the%20lower%20solar%20atmosphere%20leads%20to%20strong%20temperature%20gradients.%20%20The%20pressure%20imbalance%20following%20rapid%20heating%20drives%20fast%20flows%20of%20mass%20both%20upwards%20and%20downwards%2C%20known%20as%20chromospheric%20evaporations%20and%20condensations%2C%20respectively.%20Usually%20the%20upward%20velocity%20is%20faster%20than%20100%20km%2Fs%20and%20can%20reach%20to%20350%20km%2Fs%20in%20Fe%20XXI%201354.1%20%26Aring%3B%20line%20%28Tian%20%26amp%3B%20Chen%202018%3B%20and%20Polito%20et%20al.%202015%29%2C%20and%20500%20km%2Fs%20in%20X-ray%20%28Ning%20et%20al.%202009%2C%20%20Zhang%20%26amp%3B%20Ji%202013%29.%20In%20contrast%2C%20chromospheric%20condensations%20%28that%20propagate%20into%20denser%20plasma%29%20are%20usually%20slower%2C%20about%2010%20to%20100%20km%2Fs%28Ichimoto%20%26amp%3B%20Kurokawa%201984%3B%20Fisher%20et%20al.%201985%29.%20High%20spatial%2C%20spectral%2C%20and%20temporal%20Observations%20by%20IRIS%20found%20a%20similar%20speed%20range%20in%20Si%20IV%20and%20Mg%20II%20lines%20%28Kerr%20et%20al.%202015%3B%20Wang%20et%20al.%202023%29.%20%0A%0AIn%20this%20study%2C%20we%20present%20IRIS%20observations%20of%20a%20localized%20source%20during%20the%20X1.3%20flare%20on%202022%20March%2030.%20Spectral%20lines%20originating%20from%20this%20source%20exhibit%20extremely%20large%20red%20wings%2C%20from%20which%20we%20infer%20strong%20red-shifts%20in%20the%20transition%20region%20and%20upper%20chromosphere%20at%20speeds%20exceeding%20100%20km%2Fs.%20Figure%201%20shows%20the%20IRIS%20SJI%202796%20%26Aring%3B%20image%20alongside%20the%20light%20curves%20of%20our%20source%20of%20interest%20%28SOI%29.%20The%20SOI%20brightens%20twice%2C%20where%20the%20first%20peak%20is%20in%20response%20to%20the%20passing%20of%20the%20major%20flare%20ribbon.%20The%20second%20peak%2C%20very%20transient%2C%20is%20caused%20by%20a%20%20second%20heating%20event%2C%20that%20is%20seemingly%20associated%20with%20significantly%20faster%20downflows."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/nugget1.png","hash":"f6e0865824611aeabb042274588275a7","mimeType":"image/png","caption":"Fig.%201%20Left%20panel%3A%20IRIS%20SJI%202796%20%26Aring%3B%20at%2017%3A35%3A12%20UT.%20The%20red%20box%20indicates%20the%20source%20of%20interest%20%28SOI%29.%20Right%20panel%3A%20Light%20curves%20of%20GOES%20soft%20X-ray%20%28SXR%2C%20in%20black%29%2C%20derivative%20of%20SXR%20%28red%29%2C%20UV-2796%20in%20SOI%20%28green%29."},{"type":"text","text":"We%20used%20two%20methods%20to%20infer%20the%20magnitude%20of%20the%20chromospheric%20downflows%3A%20spectral%20moments%20and%20multiple-component%20Gaussian%20fits.%20Figure%202%20shows%20examples%20using%20multiple-component%20Gaussian%20fits%20of%20Mg%20II%2C%20C%20II%20and%20Si%20IV%20lines%20at%2017%3A35%3A19%20UT%20%28from%20when%20the%20red-wing%20asymmetry%20was%20largest%29.%20Those%20results%20suggest%20a%20large-scale%20motion%20with%20a%20speed%20up%20to%20%20160%20km%2Fs%20in%20the%20upper%20chromosphere%20and%20transition%20region.%20During%20the%20peak%20time%20%2817%3A35%3A19%20to%2017%3A35%3A29%20UT%29%2C%20the%20Mg%20II%20subordinate%20triplet%20also%20exhibit%20red-wing%20components%2C%20that%20start%20as%20separate%20components%20which%20merge%20with%20the%20stationary%20component%20%28similar%20to%20the%20chromospheric%20condensations%20studied%20by%20Graham%20et%20al%202020%2C%20though%20with%20much%20a%20larger%20Doppler%20speed%29%20.%20Their%20Doppler%20shift%20at%2017%3A35%3A19%20UT%20was%20measured%20to%20be%20130%20km%2Fs."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/nugget2.png","hash":"1f1d76799308ae54f582759f2f0c9834","mimeType":"image/png","caption":"Fig.%202%20Multi-Gaussian%20fit%20of%20UV%20spectra%20at%2017%3A35%3A19%20UT%20on%20SOI%20%28Y%20%3D%2051%20pixel%29.%20Three%20Gaussian%20components%20are%20involved%20and%20the%20combinations%20of%20all%20components%20are%20modeled%20results%20in%20red%20solid%20curves.%20The%20dotted-dash%20line%20in%20yellow%20is%20the%20red-most%20Gaussian%20fit%2C%20representing%20the%20downward%20Doppler%20velocities.%20The%20vertical%20lines%20show%20the%20rest%20line%20center%20positions%20of%20C%20II%2C%20Si%20IV%20and%20Mg%20II."},{"type":"text","text":"The%20moments%20analysis%20provides%20an%20averaged%20Doppler%20speed%20over%20the%20full%20line%20so%20yields%20smaller%20Doppler%20shifts%20for%20each%20line%20than%20the%20results%20obtained%20by%20multiple-component%20Gaussian%20fitting.%20Still%2C%20those%20moments-derived%20Doppler%20speeds%20are%20larger%20than%20typically%20observed%20flare%20sources.%20A%20histogram%20of%20Mg%20II%20Doppler%20shifts%20derived%20from%20the%20moments%20analysis%20including%20pixels%20in%20both%20SOI%20%28blue%29%20and%20the%20main%20flare%20ribbon%20%28orange%29%20is%20shown%20in%20Figure%203.%20On%20the%20flare%20ribbon%20%28pixels%2027%20to%2048%29%2C%20the%20peak%20shift%20is%20around%2030%20km%2Fs.%20Most%20of%20the%20redshifts%20of%20SOI%20pixels%20range%20from%2050%20to%20nearly%2090%20km%2Fs%20.%20For%20those%20pixels%20in%20the%20SOI%20with%20large%20moments-derived%20Doppler%20shifts%20our%20Gaussian%20fitting%20analysis%20yields%20Doppler%20motions%20far%20into%20the%20wings%2C%20up%20to%20160%20km%2Fs.%20The%20temporal%20variation%20of%20the%20Doppler%20shifts%20are%20shown%20in%20Figure%204."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/f09.png","hash":"f687c5749bca99e26f8db2b822df6c46","mimeType":"image/png","caption":"Fig.%203%20Histogram%20of%20Mg%20II%20red-shifts%20of%20pixels%20on%20flare%20ribbon%20%28orange%29%20and%20SOI%20region%20%28blue%29."},{"type":"image","file":"","url":"nuggetvideos/2023/08/25/pod_polito_vanessa_2023-08-25T21%3A28%3A28.536Z/fig_temporal.png","hash":"c717d5130a7000e205d69416d9d51d94","mimeType":"image/png","caption":"Fig.%204%20Evolution%20of%20derived%20red-shift%20velocities%2C%20using%20multi-Gaussian%20fit%20in%20panels%20%28a%29%20-%20%28d%29%20and%20spectral%20moment%20method%20in%20panel%20%28e%29%20-%20%28h%29%2C%20on%20SOI%20%28Y%20%3D%2051%20pixel%29."},{"type":"text","text":"In%20addition%20to%20the%20Mg%20II%2C%20C%20II%20and%20Si%20IV%20lines%2C%20nearby%20weaker%20lines%20are%20studied.%20The%20O%20I%20line%20at%201355.598%20%26Aring%3B%20exhibits%20no%20extraordinary%20red%20wing%20asymmetries%2C%20and%20remains%20relatively%20weak.%20As%20this%20line%20forms%20deeper%20than%20Mg%20II%20lines%2C%20the%20absence%20of%20red%20shift%20strongly%20implies%20that%20the%20unusually%20strong%20Doppler%20shift%20discussed%20above%20is%20confined%20to%20the%20transition%20region%20and%20upper%20chromosphere.%20Furthermore%2C%20the%20Mg%20II%20subordinate%20lines%20are%20strongly%20in%20emission%20and%20also%20exhibit%20asymmetries.%20This%20result%20suggests%20a%20similar%20scenario%20of%20chromospheric%20condensation%20described%20in%20Graham%20et%20al.%2C%20%282020%29.%20We%20speculate%20that%20this%20observation%20is%20an%20extreme%20example%20of%20a%20dense%20chromospheric%20condensation.%20%20%20This%20condensation%20subsequently%20propagates%20through%20the%20transition%20region%20and%20chromosphere%20but%20is%20damped%20in%20the%20mid-upper%20chromosphere.%20Its%20maximum%20speed%20is%20at%20odds%20with%20both%20typical%20observations%20and%20also%20typical%20modeling%20of%20chromospheric%20condensations.%20Though%20flare%20radiation%20hydrodynamic%20models%20do%20suggest%20such%20large%20downflowing%20velocities%20can%20be%20produced%2C%20they%20are%20thus%20far%20too%20transient%20and%20subside%20to%20a%20few%2010s%20km%2Fs%20upon%20accruing%20mass%20in%20the%20upper%20chromosphere%20%28c.f.%20the%20flare%20loop%20modeling%20review%20by%20Kerr%202022%29.%20Modeling%20of%20%20the%20flaring%20chromosphere%20should%20endeavor%20to%20explore%20the%20conditions%20%28e.g.%20an%20unusually%20low%20density%29%20that%20lead%20to%20these%20supersonic%20downflows%2C%20with%20the%20fact%20that%20this%20source%20occurred%20in%20a%20previously%20heated%20atmosphere%20is%20perhaps%20important.%20For%20more%20information%20about%20this%20work%2C%20see%20Xu%20et%20al.%202023."}],"references":["<a 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