Thermal Instability–Induced Fundamental Magnetic Field Strands in the Solar Corona

Antolin, Patrick, Martínez-Sykora, Juan and Sahin, Seray (2022) Thermal Instability–Induced Fundamental Magnetic Field Strands in the Solar Corona. The Astrophysical Journal Letters, 926 (2). L29. ISSN 2041-8205

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Thermal instability is a fundamental process of astrophysical plasmas. It is expected to occur whenever the cooling is dominated by radiation and cannot be compensated for by heating. In this work, we conduct 2.5D radiation MHD simulations with the Bifrost code of an enhanced activity network in the solar atmosphere. Coronal loops are produced self-consistently, mainly through Joule heating, which is sufficiently stratified and symmetric to produce thermal nonequilibrium. During the cooling and driven by thermal instability, coronal rain is produced along the loops. Due to flux freezing, the catastrophic cooling process leading to a rain clump produces a local enhancement of the magnetic field, thereby generating a distinct magnetic strand within the loop up to a few Gauss stronger than the surrounding coronal field. These strands, which can be considered fundamental, are a few hundred kilometers in width, span most of the loop leg, and emit strongly in the UV and extreme UV (EUV), thereby establishing a link between the commonly seen rain strands in the visible spectrum with the observed EUV coronal strands at high resolution. The compression downstream leads to an increase in temperature that generates a plume-like structure, a strongly emitting spicule-like feature, and short-lived brightening in the UV during the rain impact, providing an explanation for similar phenomena seen with IRIS. Thermal instability and nonequilibrium can therefore be associated with localized and intermittent UV brightening in the transition region and chromosphere, as well as contribute to the characteristic filamentary morphology of the solar corona in the EUV.

Item Type: Article
Additional Information: Funding information: We would like to thank the anonymous referee for the valuable contribution during the reviewing process of this manuscript. This work was supported by computational time granted from the Greek Research & Technology Network (GRNET) in the National HPC facility—ARIS. Part of the numerical computations were also carried out on the Cray XC50 at the Center for Computational Astrophysics, NAOJ. P. A. acknowledges funding from his STFC Ernest Rutherford Fellowship (No. ST/R004285/2). We gratefully acknowledge support by NASA grants 80NSSC18K1285, 80NSSC20K1272, 80NSSC21K0737, and 80NSSC21K1684 and contract NNG09FA40C (IRIS). The simulations have been run on the Pleiades cluster through computing projects s1061, s2601, and s8305 from the High End Computing (HEC) division of NASA. To analyze the data, we have used IDL. This research is also supported by the Research Council of Norway through its Centres of Excellence scheme, project No. 262622, and through grants of computing time from the Programme for Supercomputing. Data are courtesy of IRIS. IRIS is a NASA small explorer mission developed and operated by LMSAL with mission operations executed at NASA Ames Research Center and major contributions to downlink communications funded by ESA and the Norwegian Space Centre.
Uncontrolled Keywords: Plasma astrophysics, Solar corona, Solar coronal loops, Radiative magnetohydrodynamics, Solar coronal waves, Solar magnetic fields, Magnetohydrodynamical simulations, Solar prominences
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 23 Feb 2022 12:10
Last Modified: 16 Dec 2022 14:45

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