{"id":"pod_polito_vanessa_2024-12-04T21:18:59.781Z","submitter":"","author":"Ondratschek, P. [1], Przybylski, D [1]., Smitha, H. N. [1], Cameron, R. [1], Solanki, S. K. [1], Leenaarts, J. [2] [1] Max-Planck Institute for Solar System Research, 37077 Goettingen, Germany [2] Institute for Solar Physics, Department of Astronomy, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden","status":"published","creation-date":"2024-12-04T21:18:59.813Z","last-modified-date":"2025-01-12T16:41:05.75Z","credit":"","title":"Mg II h&k spectra of an enhanced network region simulated with the MURaM-ChE code: Results using 1.5D synthesis","contentBlocks":[{"type":"text","text":"Accurate%20models%20of%20the%20structure%20and%20dynamics%20of%20the%20solar%20chromosphere%20are%20necessary%20to%20understand%20the%20heating%20of%20the%20chromosphere%20and%20corona.%20The%20Mg%20II%20h%26amp%3Bk%20lines%20are%20key%20diagnostics%20of%20the%20solar%20chromosphere%20and%20are%20sensitive%20to%20the%20temperature%2C%20density%2C%20and%20nonthermal%20velocities%20in%20the%20chromosphere.%20Forward%20modeling%20of%20these%20spectral%20lines%20helps%20to%20understand%20the%20line%20formation%20and%20thus%20to%20interpret%20observations.%20Compared%20to%20observations%2C%20synthetic%20chromospheric%20lines%20typically%20show%20line%20widths%20that%20are%20too%20narrow%20and%20peak%20intensities%20that%20are%20too%20faint%20%28e.g.%2C%20Leenaarts%20et%20al.%202013b%2C%20Pereira%20et%20al.%202013%29.%20A%20closer%20match%20in%20modeling%20Mg%20II%20h%26amp%3Bk%20was%20achieved%20with%20the%20high-resolution%20simulations%20of%20Martinez-Sykora%20et%20al.%20%282023%29%20and%20the%20flux%20emergence%20simulations%20of%20Hansteen%20et%20al.%20%282023%29."},{"type":"text","text":"In%20this%20work%20%28Ondratschek%20et%20al.%202024%29%2C%20we%20use%20the%20recently%20developed%20chromospheric%20extension%20of%20the%20MURaM%20code%20%28MURaM-ChE%2C%20Przybylski%20et%20al.%202022%29%20to%20forward%20model%20the%20Mg%20II%20h%26amp%3Bk%20lines.%20The%20updated%20version%20of%20the%20code%20includes%20prescriptions%20for%20important%20NLTE%20processes%20in%20the%20chromosphere%2C%20similar%20to%20those%20in%20the%20Bifrost%20code.%20These%20include%20a%20multigroup%20scattering%20radiative%20transfer%20%28RT%29%20scheme%2C%20time-dependent%20hydrogen%20ionization%2C%20and%20radiative%20losses%20of%20strong%20chromospheric%20lines.%20We%20present%20a%20simulation%20of%20an%20enhanced%20network%20region%20in%20the%20quiet%20sun%2C%20similar%20to%20the%20public%20Bifrost%20model%20%28Carlsson%20et%20al.%202016%29.%20We%20forward%20model%20the%20Mg%20II%20h%26amp%3Bk%20lines%20by%20utilizing%20the%20RH1.5D%20code%20%28Pereira%20et%20al.%202015%2C%20Uitenbroek%202001%29.%20By%20doing%20so%2C%20each%20column%20in%20the%20atmosphere%20is%20treated%20as%20an%20independent%20plane-parallel%20atmosphere."},{"type":"image","file":"","url":"nuggetvideos/2024/12/04/pod_polito_vanessa_2024-12-04T21%3A18%3A59.781Z/iris-nugget-figure1-average-spectrum.png","hash":"8d40778e9ec2d5c37bc2866a7a36903","mimeType":"image/png","caption":"Fig.%201%3A%20Spectrum%20of%20Mg%20II%20h%20%26amp%3B%20k%20lines.%20Shown%20are%20spatial%20averages%20of%20the%20spectra%20observed%20by%20IRIS%20%28black%29%20and%20synthesized%20from%20a%20MURaM-ChE%20snapshot%20%28red%29.%20For%20comparison%2C%20we%20added%20the%20publicly%20available%20spectrum%20from%20Bifrost%20%28blue%29."},{"type":"text","text":"In%20Fig.%201%20we%20show%20spatially%20averaged%20spectra%20from%20an%20IRIS%20observation%2C%20including%20network%20fields%2C%20from%20a%20snapshot%20of%20the%20MURaM-ChE%20model%20and%20for%20comparison%20from%20the%20Bifrost%20public%20EN%20model.%20In%20the%20quiet%20Sun%2C%20the%20Mg%20II%20k%20line%20shows%20a%20number%20of%20spectral%20features%20that%20sample%20different%20heights%20in%20the%20chromosphere%3B%20a%20minimum%20in%20the%20line%20wings%20%28k1v%20and%20k1r%29%2C%20and%20two%20emission%20peaks%20%28k2v%20and%20k2r%29%20with%20a%20central%20reversal%20in%20the%20line%20core%20%28k3%29.%20We%20find%20that%20the%20spectra%20show%20a%20reasonably%20good%20match%20in%20the%20separation%20between%20the%20k1%20features%20and%20the%20overall%20line%20width.%20The%20peak%20intensities%20are%20on%20average%20higher%20than%20in%20the%20observation.%20The%20averaged%20MURaM-ChE%20spectra%20show%20a%20slightly%20larger%20blue%20asymmetry%20in%20both%20the%20Mg%20II%20k%20line%20and%20the%20Mg%20II%20h%20line%20than%20that%20seen%20in%20the%20observed%20spectra.%20This%20asymmetry%20is%20caused%20by%20the%20dominant%20area%20coverage%20by%20columns%20in%20the%20atmosphere%20that%20have%20on%20average%20downflows%20between%20the%20formation%20heights%20of%20the%20peaks%20and%20the%20central%20reversal."},{"type":"image","file":"","url":"nuggetvideos/2024/12/04/pod_polito_vanessa_2024-12-04T21%3A18%3A59.781Z/iris-nugget-figure2.png","hash":"892f03c93fdcd759b11c47f0754f4240","mimeType":"image/png","caption":"Fig.%202%3A%20Intensity%20and%20formation%20height%20at%20selected%20spectral%20features%20of%20the%20Mg%20II%20k%20line.%20The%20top%20panels%20show%20the%20brightness%20temperature%20at%20k2v%20%28panel%20a%29%2C%20k3%20%28panel%20b%29%2C%20and%20k2r%20%28panel%20c%29%20as%20classified%20by%20the%20peak-finding%20algorithm.%20The%20bottom%20panels%20show%20the%20height%20at%20an%20optical%20depth%20of%20unity%20at%20the%20wavelength%20of%20k2v%20%28panel%20d%29%2C%20k3%20%28panel%20e%29%2C%20and%20k2r%20%28panel%20f%29.%20Red%20pixels%20indicate%20those%20where%20no%20feature%20could%20be%20detected."},{"type":"text","text":"In%20Fig.%202%20intensity%20images%20at%20the%20spectral%20features%20and%20the%20formation%20heights%20%28i.e.%20%5Cbegin%7Bequation%7D%5Ctau_%7B%5Cnu%7D%3D1%5Cend%7Bequation%7D%29%20are%20shown.%20It%20can%20be%20seen%2C%20that%20the%20k2%20intensities%20are%20strongest%20above%20the%20network%20fields%20in%20the%20simulation.%20The%20formation%20height%20images%20show%20highly%20corrugated%20surfaces."},{"type":"image","file":"","url":"nuggetvideos/2024/12/04/pod_polito_vanessa_2024-12-04T21%3A18%3A59.781Z/iris-nugget-figure3.png","hash":"24c601a75ea92f9db02f14aad6a47d48","mimeType":"image/png","caption":"Fig.%203.%20Distribution%20of%20k2%20peak%20intensity%20in%20units%20of%20brightness%20temperature%20%28panel%20a%29%20and%20peak%20separation%20%28panel%20b%29%20of%20the%20Mg%20II%20k%20line%20for%20observations%20from%20IRIS%20%28black%29%20and%20the%20enhanced%20network%20model%20from%20MURaM-ChE%20%28red%29.%20For%20comparison%2C%20histograms%20of%20the%20same%20line%20parameters%20obtained%20from%20the%20Bifrost%20public%20snapshot%20have%20been%20overplotted%20in%20blue.%20For%20these%20statistics%2C%20we%20used%20the%20modeled%20spectra%20that%20are%20degraded%20to%20the%20observed%20spatial%20and%20spectral%20resolution%20for%20a%20meaningful%20comparison."},{"type":"text","text":"We%20also%20compared%20distributions%20of%20the%20k2%20peak%20intensity%20and%20peak%20separation%20%28Fig.%203%29%20between%20the%20IRIS%20observation%2C%20MURaM-ChE%2C%20and%20Bifrost.%20The%20distribution%20of%20the%20peak%20brightness%20temperatures%20in%20the%20MURaM-ChE%20model%20covers%20the%20whole%20range%20of%20observed%20values.%20The%20distribution%20from%20MURaM-ChE%20extends%2C%20however%2C%20to%20maximum%20values%2C%20which%20are%20approximately%20500%20K%20higher%2C%20and%20minimum%20values%2C%20which%20are%20approximately%20500%20K%20lower%20than%20in%20the%20observed%20distribution.%20Similar%20to%20the%20spatially%20averaged%20intensities%2C%20the%20discrepancy%20in%20the%20peak%20brightness%20temperature%20distribution%20might%20be%20a%20shortcoming%20of%20the%201.5D%20RT%20approach.%20The%20distribution%20of%20peak%20brightness%20temperature%20in%20the%20MURaM-ChE%20model%20is%20shifted%20toward%20higher%20values%20than%20in%20the%20public%20Bifrost%20snapshot.%20By%20comparing%20the%20temperature%20stratification%20between%20the%20two%20models%2C%20we%20found%20that%20the%20MURaM-ChE%20model%20shows%20higher%20temperatures%2C%20at%20column%20masses%20where%20the%20k2%20peaks%20form%2C%20than%20in%20the%20Bifrost%20model.%20The%20distribution%20of%20the%20peak%20separation%20in%20the%20MURaM-ChE%20model%20shows%20an%20overlap%20with%20the%20observed%20distribution%20but%20is%2C%20on%20average%2C%20approximately%20%5Cbegin%7Bequation%7D10%20%5C%2C%20%5Cmathrm%7Bkm%5C%2C%20s%5E%7B-1%7D%7D%5Cend%7Bequation%7D%20smaller.%20The%20peak%20separation%20in%20the%20MURaM-ChE%20is%20a%20consequence%20of%20strong%20variations%20in%20the%20line-of-sight%20%28LOS%29%20velocity%20that%20arise%20through%20shocks%20in%20the%20atmosphere.%20We%20find%20higher%20magnitudes%20of%20variations%20in%20the%20LOS%20velocity%20compared%20to%20the%20Bifrost%20model%2C%20explaining%20the%20larger%20line%20width%20and%20peak%20separation%20in%20MURaM-ChE."},{"type":"text","text":"In%20summary%2C%20we%20find%20the%20chromospheric%20extension%20of%20the%20MURaM%20code%20is%20able%20to%20produce%20a%20close%20match%20of%20the%20Mg%20II%20h%26amp%3Bk%20lines%20with%20observations.%20The%20highly%20dynamic%20atmosphere%20in%20the%20MURaM-ChE%20model%20plays%20an%20important%20role%20in%20the%20broadening%20of%20the%20spectral%20lines.%20In%20future%20studies%2C%20we%20aim%20to%20investigate%20the%20impact%20of%203D%20RT%20in%20the%20MURaM-ChE%20model%20and%20utilize%20other%20spectral%20lines%20to%20better%20understand%20the%20heating%20and%20dynamics%20of%20the%20chromosphere."},{"type":"text","text":""}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/2016A&A...585A...4C\">Carlsson, M., Hansteen, V. 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D. & Uitenbroek, H. 2015, A&A, 574, A3</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2022A&A...664A..91P\">Przybylski, D., Cameron, R., Solanki, S. K., et al. 2022, Astronomy and Astrophysics, 664, A91</a>","",""],"pubDate":"2025-01-12T18:19:13.221Z"}