Tuesday

Acoustic waves excited in the photosphere and below might play an integral part in the heating of the solar 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, and conversion in the lower layers of the solar atmosphere using 3D numerical MHD simulations. A numerically relaxed model of a gravitationally stratified expanding straight coronal loop, stretching from photosphere to photosphere, is perturbed at one footpoint by a periodic acoustic driver with a period of 370 seconds. For this period acoustic cutoff regions are present below the transition region. About 2% of the initial energy from the driver reach the corona. The shape of the cutoff regions and the height of the transition region show a highly dynamic behavior in the simulations. 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 transition region. These standing waves cause an oscillation of the transition region height. Comparison of the waves occurring in the simulations with the tube wave theory of a simplified model reveals the possibility that the originally plane waves converted to sausage surface waves between cutoff region and transition region and to sausage body waves above the transition region.​