IRIS Nugget
Welcome to the IRIS Science Nuggets: highlights of recent IRIS scientific results for the solar physics community.
{"id":"pod_polito_vanessa_2024-04-30T17:03:48.045Z","submitter":"Souvik Bose","author":"Souvik Bose[1,2,3,4], Bart De Pontieu[1,3,4], Viggo Hansteen[1,2,3,4], Alberto Sainz Dalda[1,2], Sabrina Savage[5] & Amy Winebarger[5]","status":"published","creation-date":"2024-04-30T17:03:48.072Z","last-modified-date":"2024-05-13T22:37:20.762Z","credit":"[1] Lockheed Martin Solar & Astrophysics Lab, CA, USA [2] Bay Area Environmental Research Institute, CA, USA [3] Institute of Theoretical Astrophysics, University of Oslo, Norway [4] Rosseland Centre for Solar Physics, University of Oslo, Norway [5] NASA Marshall Space Flight Center, Huntsville, AL, USA","title":"Chromospheric and coronal heating in an active region plage by dissipation of currents from braiding","contentBlocks":[{"type":"text","text":"The%20question%20of%20what%20heats%20the%20outer%20solar%20atmosphere%20has%20been%20a%20long-standing%20mystery%20in%20astrophysics%20since%20the%201940s%20%28Edlen%201942%29.%20Several%20physical%20mechanisms%20have%20been%20proposed%20to%20explain%20the%20heating%2C%20including%20waves%20and%20magnetic%20reconnection.%20However%2C%20the%20challenge%20is%20to%20determine%20the%20dominant%20heat%20source%20in%20different%20regions%20on%20the%20Sun%2C%20both%20in%20general%20and%20in%20specific%20scenarios.%20Statistical%20studies%20of%20Sun-like%20stars%20reveal%20a%20correlation%20between%20global%20chromospheric%20and%20coronal%20emissions%2C%20constraining%20theoretical%20models%20of%20potential%20heating%20mechanisms.%20However%2C%20spatially%20resolved%20observations%20of%20the%20Sun%20have%20surprisingly%20failed%20to%20show%20a%20similar%20correlation%20on%20small%20spatial%20scales.%20%0A%0AThe%20present%20study%20%28Bose%20et%20al.%202024%29%20aims%20at%20unravelling%20the%20physical%20processes%20responsible%20for%20heating%20of%20the%20%26quot%3Bmoss%26quot%3B%20regions%20that%20lie%20at%20the%20footpoints%20of%20active%20region%20loops%20at%20%28sub%29arcsecond%20scales%20using%20unique%20coordinated%20observations%20from%20the%20High-resolution%20Coronal%20Imager%20%28HiC2.1%29%20and%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29%2C%20and%20a%203D%20MHD%20simulation%20of%20an%20active%20region.%20Upper%20transition%20region%20%28TR%29%20moss%20provides%20an%20excellent%20laboratory%20to%20study%20how%20chromospheric%20and%20coronal%20heating%20mechanisms%20are%20spatio-temporally%20correlated.%20Figure%201%20shows%20an%20overview%20of%20the%20chromospheric%20and%20coronal%20observations%2C%20and%20the%20derived%20chromospheric%20thermodynamic%20parameters%20from%20the%20IRIS2%2B%20inversion%20database%20%28Sainz%20Dalda%20et%20al.%202024%29."},{"type":"image","file":"","url":"nuggetvideos/2024/04/30/pod_polito_vanessa_2024-04-30T17%3A03%3A48.045Z/Screenshot 2024-05-13 at 02.51.01.png","hash":"2a6f363d8417e32cf035f04bd58aef10","mimeType":"image/png","caption":"Figure%201%3A%20Chromospheric%20%28panels%20c--e%29%20and%20coronal%20scenery%20%28panels%20a%20and%20b%29%20of%20the%20moss%20observed%20with%20IRIS%20and%20HiC2.1%20on%2029%20May%202018.%20The%20inverted%20and%20the%20observed%20IRIS%20Mg%20II%20h%26amp%3Bk%20spectra%20%28panel%20f%29%20and%20the%20recovered%20thermodynamic%20parameters%20%28panels%20g--i%29%20show%20that%20the%20chromosphere%20underneath%20the%20moss%20is%20hotter%20compared%20with%20the%20surrounding%20regions."},{"type":"text","text":"Our%20observations%20show%20a%20remarkable%20correlation%2C%20on%20spatial%20scales%20down%20to%20a%20few%20hundred%20kilometres%20on%20the%20surface%20of%20the%20Sun%2C%20between%20heating%20in%20the%20chromosphere%20and%20emission%20in%20the%20upper%20transition%20region%2Flower%20corona%20in%20a%20plage%20region%20as%20shown%20in%20Figure%202.%20This%20is%20in%20contrast%20with%20earlier%20results%20%28such%20as%2C%20De%20Pontieu%20et%20al.%201999%2C%202003%29%20where%20the%20authors%20failed%20to%20obtain%20such%20a%20correlation%20likely%20due%20to%20the%20fact%20that%20the%20chromospheric%20emission%20in%20these%20early%20studies%2C%20obtained%20using%20broadband%20Ca%20II%20396%20nm%20images%2C%20was%20not%20really%20a%20signature%20of%20true%20chromospheric%20heating%20but%20rather%20emanates%20from%20deeper%2C%20hotter%20layers%20in%20the%20convection%20zone.%20Moreover%2C%20we%20show%20a%20tight%20correlation%20between%20the%20derived%20chromospheric%20heating%20signatures%20%28e.g.%20using%20plasma%20temperature%20and%20electron%20densities%2C%20right%20panel%20of%20Figure%202%29%20rather%20than%20focusing%20on%20the%20proxies%20of%20the%20chromospheric%20heating%20signatures%2C%20which%20is%20a%20major%20advanced%20compared%20with%20the%20early%20studies.%20%0A%0AFurthermore%2C%20analysis%20of%20the%20correlation%20between%20the%20derived%20thermodynamic%20parameters%20with%20the%20lower%20coronal%20%28HiC%29%20emission%20as%20a%20function%20of%20height%20%28optical%20depth%29%20in%20the%20solar%20atmosphere%20shows%20that%20there%20exists%20a%20range%20of%20optical%20depths%20within%20which%20the%20correlation%20coefficients%20are%20relatively%20high%20%28i.e.%20roughly%20down%20to%20the%20temperature%20minimum%2C%20see%20Figure%203%29.%20This%20tight%20coupling%20weakens%20deeper%20in%20the%20solar%20atmosphere%20%28beyond%20the%20temperature%20minimum%29%20suggesting%20different%20physical%20conditions%20of%20the%20plasma.%20However%2C%20there%20is%20no%20doubt%20that%20hot%20and%20dense%20plasma%20dominates%20the%20lower%20to%20upper%20chromosphere%20underneath%20and%20is%20well%20correlated%20with%20upper%20TR%2Flower%20coronal%20moss%20locations."},{"type":"image","file":"","url":"nuggetvideos/2024/04/30/pod_polito_vanessa_2024-04-30T17%3A03%3A48.045Z/Screenshot 2024-05-13 at 13.16.35.png","hash":"4505fb1ecfe78e1114500c2d6a0aa448","mimeType":"image/png","caption":"Figure%202%3A%20Spatio-temporal%20correlation%20between%20heating%20in%20the%20chromosphere%20and%20the%20emission%20in%20the%20upper%20TR%2Flower%20coronal%20moss%20at%20subacrsecond%20scales.%20Left%20panel%3A%20correlation%20between%20the%20enhanced%20intensities%20observed%20in%20the%20chromosphere%20and%20the%20corona%3B%20right%20panel%3A%20observed%20correlation%20between%20the%20derived%20chromospheric%20thermodynamic%20parameters%20and%20the%20emission%20seen%20by%20HiC%20in%20the%20same%20format%20as%20the%20left%20panel."},{"type":"image","file":"","url":"nuggetvideos/2024/04/30/pod_polito_vanessa_2024-04-30T17%3A03%3A48.045Z/Screenshot 2024-05-13 at 13.47.26.png","hash":"1641ba81275c946a3c40e5d9d2d1690e","mimeType":"image/png","caption":"Figure%203%3A%20Heatmaps%20showing%20the%20depth-dependent%20correlation%20for%20ROI-B.%20Left%20panel%3A%20Correlation%20coefficients%20between%20the%20temperature%20and%20HiC%20emission%20as%20a%20function%20of%20optical%20depths%20%5Cbegin%7Bequation%7D%20%28log%5Ctau%29%20%5Cend%7Bequation%7D%20and%20time%20%28%23raster%29.%20Right%20panel%3A%20same%20but%20for%20the%20correlation%20between%20electron%20densities%20%5Cbegin%7Bequation%7D%20%28N_%7Be%7D%29%20%5Cend%7Bequation%7D%20and%20HiC%20emission.%20The%20horizontal%20dashed%20lines%20in%20the%20two%20panels%20show%20the%20upper%20and%20lower%20limit%20of%20the%20sensitivies%20of%20the%20spectral%20inversion."},{"type":"text","text":"The%20tight%20correlation%20between%20the%20derived%20physical%20parameters%20with%20the%20HiC%20intensity%20down%20to%20the%20temperature%20minimum%20strongly%20suggests%20the%20prevalence%20of%20a%20local%20heating%20mechanism%20in%20these%20regions.%20Thermal%20conduction%2C%20which%20obviously%20plays%20a%20role%20in%20the%20hot%20corona%20and%20upper%20TR%2C%20is%20negligible%20at%20low%20temperatures%20in%20the%20lower%20chromosphere%20and%20thus%20cannot%20fully%20explain%20the%20observed%20spatio-temporal%20correlation.%20Thanks%20to%20the%20advanced%203D-MHD%20simulation%20of%20an%20active%20region%20plage%2C%20computed%20using%20the%20Bifrost%20code%2C%20we%20find%20that%20our%20observations%20are%20compatible%20with%20a%20scenario%20in%20which%20the%20dissipation%20of%20electrical%20currents%20caused%20by%20reconnection%20from%20braiding%20of%20magnetic%20fields%20is%20responsible%20for%20heating%20the%20plasma%20simultaneously%20to%20chromospheric%20and%20coronal%20temperatures%20%28see%20Figure%204%29.%20This%20braiding%20of%20field%20lines%20occurs%20in%20response%20to%20shuffling%20of%20the%20field%20by%20convective%20flows%20at%20the%20surface%20originally%20proposed%20by%20Parker%201983.%20Our%20analysis%20also%20suggests%20that%20alternative%20heating%20mechanisms%2C%20such%20as%20Alfven%20wave%20turbulence%20%28van%20Ballegooijen%20et%20al.%202017%29%20and%20energy%20deposition%20of%20sudden%20bursts%20of%20accelerated%20non-thermal%20electrons%20%28Testa%20et%20al.%202013%29%2C%20seem%20less%20likely%20to%20cause%20the%20observed%20heating%20patterns."},{"type":"image","file":"","url":"nuggetvideos/2024/04/30/pod_polito_vanessa_2024-04-30T17%3A03%3A48.045Z/Screenshot 2024-05-13 at 14.08.00.png","hash":"7b5583750b2c42daf27d0a4823258549","mimeType":"image/png","caption":"Figure%204%3A%203D%20MHD%20simulation%20of%20an%20active%20region%20plage%20shows%20the%20presence%20of%20current%20sheets%20traversing%20the%20chromosphere%20and%20the%20corona.%20They%20are%20caused%20due%20to%20braiding%20of%20the%20magnetic%20field%20lines%20close%20to%20the%20footpoints.%20The%20dissipation%20of%20these%20current%20sheets%20through%20Joule%20heating%20causes%20enhanced%20emission%20in%20the%20synthetic%20Mg%20II%20k3%20and%20172%20angstrom%20images%20shown%20in%20panels%20%28b%29%20and%20%28c%29."},{"type":"text","text":"Our%20results%20represent%20a%20significant%20advance%20in%20understanding%20the%20heating%20of%20the%20chromosphere%20and%20the%20upper%20transition%20region%20and%20lower%20corona%20of%20some%20of%20the%20strongest%20magnetic%20field%20regions%20on%20the%20Sun.%20However%2C%20to%20understand%20how%20widespread%20this%20heating%20mechanism%20is%20on%20the%20Sun%2C%20longer%20duration%20coronal%20observations%20will%20be%20necessary%2C%20which%20will%20thankfully%20be%20available%20from%20the%20EUI%20telescope%20on-board%20ESA%27s%20Solar%20Orbiter%20mission%20and%20in%20the%20future%20with%20NASA%20MUSE%20mission.%20Combining%20these%20observations%20with%20measurements%20from%20meter-class%20ground%20based%20telescopes%20such%20as%20SST%20and%20DKIST%20will%20enable%20us%20to%20obtain%20further%20crucial%20insights%20into%20the%20nature%20of%20this%20problem."}],"references":["<a href=\"https://ui.adsabs.harvard.edu/abs/1943ZA.....22...30E/abstract\">Edlen, B., Zeit. Astrophys, 22 (1942)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2024NatAs.tmp...66B/abstract\">Bose, S. et al., Nature Astronomy, 66B (2024)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2024ApJS..271...24S/abstract\">Sainz Dalda, A. et al., ApJ, 271 (2024)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1999SoPh..190..419D/abstract\">De Pontieu, B. et al., Sol. Phys, 190 (1999)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2003ApJ...590..502D/abstract\">De Pontieu, B. et al., ApJ, 590 (2003)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/1983ApJ...264..635P/abstract\">Parker, E. N., ApJ, 264 (1983)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2017ApJ...849...46V/abstract\">van Ballegooijen, A. A., ApJ, 849 (2017)</a>","<a href=\"https://ui.adsabs.harvard.edu/abs/2013ApJ...770L...1T/abstract\">Testa, P. et al, ApJ, 770 (2013)</a>","",""],"pubDate":"2024-05-13T22:39:57.216Z"}