Acoustic wave propagation in the solar atmosphere. IV Nonadiabatic wave excitation with frequency spectra

TL;DR

This study investigates how large amplitude acoustic waves with radiation damping influence the solar atmosphere, revealing a critical frequency for resonance behavior and showing that spectral shape affects temperature distributions and dominant oscillation bands.

Contribution

It introduces a non-adiabatic model of acoustic wave excitation in the solar atmosphere, identifying a critical frequency and demonstrating the impact of spectral shape on atmospheric dynamics.

Findings

Resonance behavior depends on a critical frequency of ~1/25 Hz.

Persistent resonance oscillations occur for frequencies above the critical.

At greater heights, a 3-minute oscillation band becomes dominant.

Abstract

We study the response of the solar atmosphere to excitations by large amplitude acoustic waves with radiation damping now included. Monochromatic adiabatic waves, due to unbalanced heating, generate continuously rising chromospheric temperature plateaus in which the low frequency resonances quickly die out. All non-adiabatic calculations lead to stable mean chromospheric temperature distributions determined by shock dissipation and radiative cooling. For non-adiabatic monochromatic wave excitation, a critical frequency f_cr ~ 1/25 Hz is confirmed, which separates domains of different resonance behaviour. For waves of frequency f < f_cr, the resonances decay, while for waves of f > f_cr persistent resonance oscillations occur, which are perpetuated by shock merging. Excitation with acoustic frequency spectra produces distinct dynamical mean chromosphere models where the detailed temperature distributions depend on the shape of the assumed spectra. The stochasticity of the spectra and the ongoing shock merging lead to a persistent resonance behaviour of the atmosphere. The acoustic spectra show a distinct shape evolution with height such that at great height a pure 3 min band becomes increasingly dominant. With our Eulerian code we did not find appreciable mass flows at the top boundary.