A New Look at Mode Conversion in a Stratified Isothermal Atmosphere

TL;DR

This paper investigates mode conversion of waves in a stratified isothermal atmosphere with a vertical magnetic field, combining numerical and analytical methods to understand wave behavior from low to high-beta plasma regions.

Contribution

It provides a detailed analysis of downward wave propagation and mode conversion in a simplified model, extending previous upward-propagation studies.

Findings

Derived a simple expression for transmitted wave amplitude.

Numerical and analytical results show good agreement.

Enhanced understanding of wave mode conversion mechanisms.

Abstract

Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-beta plasma to a high-beta plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere, with a uniform, vertical magnetic field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov: Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this paper studies the downward propagation of waves from a low-beta to high-beta environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution.