The evolution of the coronal loop structure due to the phase mixing of high and low-frequency Alfvén waves

Abstract

ABSTRACT Coronal loops are known to host Alfvén waves propagating in the corona from the lower layers of the solar atmosphere and because of their internal structure, phase mixing is likely to occur. The structure of the coronal loop could be significantly affected by the thermodynamic feedback of the heating generated by phase mixing. However, this phenomenon can be sensitive to the period of the propagating Alfvén waves due to how short period waves can be easily dissipated and the way long-period waves may accumulate considerable energy in resonating coronal loops. Using the Lare2d code, a coronal loop model of a field-aligned thermodynamic equilibrium and a cross-field background heating profile is created, with an additional forcing term added to drive Alfvén waves with coronal amplitudes between $5{\!-\!}30 \, \mathrm{km} \, \mathrm{s}^{-1}$. We show that high-frequency waves can generate heating corresponding to a ${\sim} 10~{{\ \rm per\ cent}}$ increase of the initial coronal shell temperature, chromospheric upflows of up to $0.6 \, \mathrm{km} \, \mathrm{s}^{-1}$ and a coronal shell mass increase of ${\sim} 15~{{\ \rm per\ cent}}$. These changes are sufficient to alter and maintain a new coronal loop density structure, broadening the region where efficient phase mixing (and therefore heating) occurs. In contrast, low-frequency waves are unable to be effectively dissipated, resulting in minimal changes to the loop structure. We see little evidence of wave energy accumulation in the corona and are unable to conclude that the dissipation of low-frequency Alfvén waves can be an effective heating mechanism in coronal loops in the setup used in this study.