Three-dimensional modeling of the Ca II H and K lines in the solar atmosphere

Bjørgen, Johan Pires; Sukhorukov, A. P.; Leenaarts, J.; Carlsson, Mats; Scharmer, G.; Hansteen, V. H.

doi:10.1051/0004-6361/201731926

Cited by 72 publications

(90 citation statements)

References 68 publications

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“…The emergent intensities in the diagnostics sensitively depend on the temperature and electron density. Comparison of models with observations (such as in Leenaarts et al 2013;Bjørgen et al 2018) show that current models are not getting the intensities right, and that they need to be refined. The treatment of chromospheric radiative energy exchange is very likely one of the aspects in need of further improvement.…”

Section: Discussionmentioning

confidence: 99%

Radiation hydrodynamics in simulations of the solar atmosphere

Leenaarts

2020

Living Rev Sol Phys

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Nearly all energy generated by fusion in the solar core is ultimately radiated away into space in the solar atmosphere, while the remaining energy is carried away in the form of neutrinos. The exchange of energy between the solar gas and the radiation field is thus an essential ingredient of atmospheric modeling. The equations describing these interactions are known, but their solution is so computationally expensive that they can only be solved in approximate form in multi-dimensional radiation-MHD modeling. In this review, I discuss the most commonly used approximations for energy exchange between gas and radiation in the photosphere, chromosphere, and corona.

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Section: Discussionmentioning

confidence: 99%

Radiation hydrodynamics in simulations of the solar atmosphere

Leenaarts

2020

Living Rev Sol Phys

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“…1 from Leenaarts et al (2013b) or Fig. 15 from Bjørgen et al (2018)), this should help the inversions. Moreover, finding an atmospheric model that can explain also the UV part of an Ellerman bomb is of great interest.…”

Section: Inversions Of Combined Sst and Iris Datamentioning

confidence: 99%

Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations

Vissers

Rodríguez

Libbrecht

et al. 2019

A&A

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Ellerman bombs and UV bursts are transient brightenings that are ubiquitously observed in the lower atmospheres of active and emerging flux regions. As they are believed to pinpoint sites of magnetic reconnection in reconfiguring fields, understanding their occurrence and detailed evolution may provide useful insights in the overall evolution of active regions. Here we present results from inversions of SST/CRISP and CHROMIS, as well as IRIS data of such transient events. Combining information from the Mg ii & k, Si iv and Ca ii 8542 Å and Ca ii H & K lines, we aim to characterise their temperature and velocity stratification, as well as their magnetic field configuration. We find average temperature enhancements of a few thousand kelvin close to the classical temperature minimum, similar to previous studies, but localised peak temperatures of up to 10,000-15,000 K from Ca ii inversions. Including Mg ii appears to generally dampen these temperature enhancements to below 8000 K, while Si iv requires temperatures in excess of 10,000 K at low heights, but may also be reproduced with secondary temperature enhancements of 35,000-60,000 K higher up. However, reproducing Si iv comes at the expense of overestimating the Mg ii emission. The line-of-sight velocity maps show clear bi-directional jet signatures for some events and strong correlation with substructure in the intensity images in general. Absolute lineof-sight velocities range between 5-20 km s −1 on average, with slightly larger velocities towards the observer than away. The inverted magnetic field parameters show an enhancement of the horizontal field co-located with the brightenings at heights similar to that of the temperature increase. We are thus able to largely reproduce the observational properties of Ellerman bombs with UV burst signature (e.g. intensities, profile asymmetries, morphology and bi-directional jet signatures) with temperature stratifications peaking close to the classical temperature minimum. Correctly modelling the Si iv emission in agreement with all other diagnostics is, however, an outstanding issue and remains paramount in explaining its apparent coincidence with Hα emission. Fine-tuning the approach (accounting for resolution differences, fitting localised temperature enhancements and/or performing spatially-coupled inversions) is likely necessary in order to obtain better agreement between all considered diagnostics.

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“…Finally, for Ca ii we used the five-level plus continuum model atom of Bjørgen et al (2018) where we similarly treat only Ca ii K in PRD and Ca ii H in CRD.…”

Section: Model Atomsmentioning

confidence: 99%

“…Both the Mg ii h&k and Ca ii H&K lines have the ground state as their lower level, so their opacity scales approximately with the density as long as Mg ii and Ca ii are the dominant ionization stage. As Mg ii is 18 times more abundant than Ca ii, the line cores of Mg ii h&k are formed a few scale heights higher up in the chromosphere than the line cores of Ca ii H&K (Leenaarts et al 2013b;Bjørgen et al 2018).…”

Section: Formation Heightsmentioning

confidence: 99%

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Three-dimensional modeling of chromospheric spectral lines in a simulated active region

Bjørgen

Leenaarts

Rempel

et al. 2019

A&A

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Context. Because of the complex physics that governs the formation of chromospheric lines, interpretation of solar chromospheric observations is difficult. The origin and characteristics of many chromospheric features are, because of this, unresolved. Aims. We focus here on studying two prominent features: long fibrils and flare ribbons. To model them, we use a 3D MHD simulation of an active region which self-consistently reproduces both of them. Methods. We model the Hα, Mg ii k, Ca ii K, and Ca ii 8542 Å lines using the 3D non-LTE radiative transfer code Multi3D. To obtain non-LTE electron densities, we solve the statistical equilibrium equations for hydrogen simultaneously with the charge conservation equation. We treat the Ca ii K and Mg ii k lines with partially coherent scattering.Results. This simulation reproduces long fibrils that span between the opposite-polarity sunspots and go up to 4 Mm in height. They can be traced in all lines due to density corrugation. Opposite to previous studies, Hα, Mg ii h&k, and Ca ii H&K, are formed at similar height in this model. Although, some of the high fibrils are also visible in the Ca ii 8542 Å line, this line tend to sample loops and shocks lower in the chromosphere. Magnetic field lines are aligned with the Hα fibrils, but the latter holds to a lesser extent for the Ca ii 8542 Å line. The simulation shows structures in the Hα line core that look like flare ribbons. The emission in the ribbons is caused by a dense chromosphere and a transition region at high column mass. The ribbons are visible in all chromospheric lines, but least prominent in Ca ii 8542 Å line. In some pixels, broad asymmetric profiles with a single emission peak are produced, similar to the profiles observed in flare ribbons. They are caused by a deep onset of the chromospheric temperature rise and large velocity gradients. Conclusions. The simulation produces long fibrils similar to what is seen in observations. It also produces structures similar to flare ribbons despite the lack of non-thermal electrons in the simulation. The latter suggests that thermal conduction might be a significant agent in transporting flare energy to the chromosphere in addition to non-thermal electrons.

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Three-dimensional modeling of the Ca II H and K lines in the solar atmosphere

Cited by 72 publications

References 68 publications

Radiation hydrodynamics in simulations of the solar atmosphere

Radiation hydrodynamics in simulations of the solar atmosphere

Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations

Three-dimensional modeling of chromospheric spectral lines in a simulated active region

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