Acoustic wave properties in footpoints of coronal loops in 3D MHD simulations

TL;DR

This study uses 3D MHD simulations to analyze how acoustic waves propagate, damp, and convert in coronal loops, revealing that only a small fraction of wave energy reaches the corona and identifying wave behaviors related to the cutoff regions.

Contribution

It provides detailed insights into wave transmission, damping, and mode conversion in coronal loops using realistic 3D MHD simulations, highlighting dynamic cutoff regions and wave interactions.

Findings

Only about 2% of wave energy reaches the corona.

Waves are propagating below and above cutoff, but evanescent within.

Standing waves cause oscillations of the transition region.

Abstract

Acoustic waves excited in the photosphere and below might play an integral part in the heating of the solar chromosphere and corona. However, it is yet not fully clear how much of the initially acoustic wave flux reaches the corona and in what form. We investigate the wave propagation, damping, transmission, and conversion in the lower layers of the solar atmosphere using 3D numerical MHD simulations. A model of a gravitationally stratified expanding straight coronal loop, stretching from photosphere to photosphere, is perturbed at one footpoint by an acoustic driver with a period of 370 seconds. For this period acoustic cutoff regions are present below the transition region (TR). About 2% of the initial energy from the driver reach the corona. The shape of the cutoff regions and the height of the TR show a highly dynamic behavior. Taking only the driven waves into account, the waves have a propagating nature below and above the cutoff region, but are standing and evanescent within the cutoff region. Studying the driven waves together with the background motions in the model reveals standing waves between the cutoff region and the TR. These standing waves cause an oscillation of the TR height. In addition, fast or leaky sausage body-like waves might have been excited close to the base of the loop. These waves then possibly convert to fast or leaky sausage surface-like waves at the top of the main cutoff region, followed by a conversion to slow sausage body-like waves around the TR.