Abstract
The quantification of all possible waves and instabilities in any given system is of paramount importance, and knowledge of the full magnetohydrodynamic (MHD) spectrum allows one to predict the (in)stability of a given equilibrium state. This is highly relevant in many (astro)physical disciplines, and when applied to the solar atmosphere it may yield various new insights in processes such as prominence formation and coronal-loop oscillations. In this work we present a detailed, high-resolution spectroscopic study of the solar atmosphere, where we use our newly developed Legolas code to calculate the full spectrum with corresponding eigenfunctions of equilibrium configurations that are based on fully realistic solar atmospheric models, including gravity, optically thin radiative losses, and thermal conduction. Special attention is given to thermal instabilities, known to be responsible for the formation of prominences, together with a new outlook on the thermal and slow continua and how they behave in different chromospheric and coronal regions. We show that thermal instabilities are unavoidable in our solar atmospheric models and that there exist certain regions where the thermal, slow, and fast modes all have unstable wave-mode solutions. We also encounter regions where the slow and thermal continua become purely imaginary and merge on the imaginary axis. The spectra discussed in this work illustrate clearly that thermal instabilities (both discrete and continuum modes) and magneto-thermal overstable propagating modes are ubiquitous throughout the solar atmosphere, and they may well be responsible for much of the observed fine-structuring and multi-thermal dynamics.
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Acknowledgments
This work is supported by funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme, Grant agreement No. 833251 PROMINENT ERC-ADG 2018; by the VSC (Flemish Supercomputer Center), funded by the Research Foundation – Flanders (FWO) and the Flemish Government – department EWI; and by internal funds KU Leuven, project C14/19/089 TRACESpace.
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This article belongs to the Topical Collection:
Magnetohydrodynamic (MHD) Waves and Oscillations in the Sun’s Corona and MHD Coronal Seismology
Guest Editors: Dmitrii Kolotkov and Bo Li
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Claes, N., Keppens, R. Magnetohydrodynamic Spectroscopy of a Non-adiabatic Solar Atmosphere. Sol Phys 296, 143 (2021). https://doi.org/10.1007/s11207-021-01894-2
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DOI: https://doi.org/10.1007/s11207-021-01894-2