Can we rely on EUV emission to identify coronal waveguides?

Abstract

Traditional models of coronal oscillations rely on modelling the coronal structures that support them as compact cylindrical waveguides. Recently, an alternative model of the structure of the corona has been proposed, where the thin strand-like coronal loops observable in the EUV emission are a result of line-of-sight integration of warps in more complex coronal structures, referred to as the coronal veil model. We extend the implications of the coronal veil model of the solar corona to models of coronal oscillations. Using the convection-zone-to-corona simulations with the radiation-magnetohydrodynamics code Bifrost, we analysed the structure of the self-consistently formed simulated corona. We focus on the spatial variability of the volumetric emissivity of the Fe IX 171.073 Å EUV line, and on the variability of the Alfvén speed, which captures the density and magnetic structuring of the simulated corona. We traced features associated with large magnitudes of the Alfvén speed gradient, which are the most likely to trap MHD waves and act as coronal waveguides, and looked for the correspondence with emitting regions which appear as strand-like loops in line-of-sight-integrated EUV emission. The waveguide filling factors corresponding to the fraction of the waveguides filled with plasma emitting in the given EUV wavelength range from 0.09 to 0.44. This suggests that we can observe only a small fraction of the waveguide. Similarly, the projected waveguide widths in the plane of the sky are several times larger than the widths of the apparent loops observable in EUV. We conclude that the 'coronal veil' structure is model-independent. As a result, we find a lack of straightforward correspondence between a peak in the integrated emission profile which constitutes an apparent coronal loop and regions of plasma bound by a large Alfvén speed gradient acting as waveguides.

8 pages, 7 figures, accepted for publication in A&A

References in corpus (15)

• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Fine strand-like structure in the solar corona from MHD transverse oscillations
• Unresolved fine-scale structure in solar coronal loop-tops
• Wave heating in gravitationally stratified coronal loops in the presence of resistivity and viscosity
• Fundamental-Mode Oscillations of Two Coronal Loops within a Solar Magnetic Arcade
• First Perihelion of EUI on the Solar Orbiter mission
• Self-consistent 3D radiative MHD simulations of coronal rain formation and evolution
• Traveling kink oscillations of coronal loops launched by a solar flare
• Resonant absorption in expanding coronal magnetic flux tubes with uniform density
• Prevalence of Thermal Non-Equilibrium over an Active Region
• EUV fine structure and variability associated with coronal rain revealed by Solar Orbiter/EUI HRIEUV and SPICE
• Deciphering the solar coronal heating: Energizing small-scale loops through surface convection
• Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere
• Do Coronal Loops Oscillate in Isolation?
• Damping of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere