On the Theory of Absorption of Sound Waves via the Bulk Viscosity in the Partially Ionized Solar Chromosphere

TL;DR

This paper investigates how bulk viscosity contributes to the damping of sound waves in the partially ionized solar chromosphere, providing a quantitative estimate of the energy flux needed for heating and emphasizing the importance of volume viscosity.

Contribution

It introduces a detailed calculation of bulk viscosity effects in the solar chromosphere and demonstrates its dominance in acoustic wave damping for chromosphere heating.

Findings

Bulk viscosity is the primary damping mechanism for acoustic waves.

Estimated sound wave energy flux needed for heating is approximately 320 kW/m$^2$.

Volume viscosity alone suffices for chromosphere heating without artificial viscosity.

Abstract

Bulk viscosity and thermodynamic variables of a hydrogen-helium cocktail: internal energy, enthalpy, pressure, their derivatives, heat capacities per constant density and pressure are obtained using temperature and density height profiles of the solar atmosphere [Avrett & Loeser, ApJS Vol. 175, 229 (2008)]. The qualitative evaluation for the necessary sound wave energy flux to heat the solar chromosphere is determined to be 320 kW/m$^2$. It is concluded that the bulk viscosity creates the dominating mechanism of acoustic waves damping and it is not necessary to introduce artificial viscosity or to conclude that shear viscosity is not sufficient for chromosphere heating; the volume viscosity induced wave absorption is sufficient.