Acoustic-Gravity Waves as a Probe of the Dynamics of the Solar Atmosphere

The solar atmosphere is a highly dynamic region of the sun that exhibits an enigmatic temperature structure. It is also home to solar eruptive events that pose challenges in their prediction. One mechanism under consideration for the heating of the atmosphere is mechanical heating by waves generated by the turbulent convection near the star's surface. When these waves, which include acoustic waves and internal gravity waves, propagate into the star's atmosphere, they can deposit the convective energy they are carrying via shock formation and wave breaking. However, a considerable amount of the mechanical energy in the waves can be lost by radiative damping in the lowest layers of the atmosphere. Hence, the radiative damping time (TR) is crucial in understanding the energy budget of solar atmospheric heating. Furthermore, eruptive events are accompanied by strong and highly inclined magnetic fields. Such magnetic fields cause a change in the acoustic cutoff frequency (ACF), allowing previously trapped low-frequency acoustic waves to now propagate freely into the solar atmosphere. The variations in ACF could be an effective precursor to eruptive events. Acoustic-gravity waves traveling in the solar atmosphere can be used as a probe to map the TR and ACF. This is achieved using wave propagation models (Souffrin 1972; Mihalas & Toomre 1981) in concert with observed phase lags between vertical velocity perturbations at different heights in the solar atmosphere. We also present a modified wave propagation model, that serves additionally as evidence for wave reflection in the solar atmosphere. TR and ACF have been only extensively studied as a function of height in the solar atmosphere, but here we analyze them spatially.