Fast Magnetoacoustic Wave Behavior within Gravitationally Stratified, Magnetically Inhomogeneous Media

TL;DR

This paper explores how gravitational stratification and magnetic inhomogeneity affect fast magnetoacoustic waves in the solar atmosphere, revealing new phenomena like caustics and cusps through combined numerical and analytical methods.

Contribution

It introduces a combined numerical and semi-analytical approach to study wave behavior in stratified, inhomogeneous media, highlighting effects of stratification on wave refraction and symmetry breaking.

Findings

Stratification causes significant refraction and symmetry breaking.

Formation of caustic surfaces and cusps in wave patterns.

Strong agreement between numerical simulations and analytical solutions.

Abstract

The nature of MHD waves within inhomogeneous media is fundamental to understanding and interpreting wave behavior in the solar atmosphere. We investigate fast magnetoacoustic wave behavior within gravitationally stratified, magnetically inhomogeneous media, by studying a magnetic environment containing a simple 2D X-type magnetic null point. The addition of gravitational stratification fundamentally changes the nature of the system, including breaking the symmetry. There are two main governing effects: the stratified density profile acts in combination with the inhomogeneous magnetic field, creating a large gradient in the Alfven speed and hence a system replete with refraction. The system is investigated using both numerical simulations and a semianalytical WKB solution (via Charpit's method and a fourth-order Runge-Kutta solver) and we find strong agreement between both. The results show a fundamental difference between the stratification-free and stratified cases, including the formation of caustic surfaces and cusps, and we contextualize these results in the theoretical understanding of fast magnetoacoustic waves.