Theoretical modeling of propagation of magneto-acoustic waves in magnetic regions below sunspots

TL;DR

This study uses numerical simulations and eikonal approximation to analyze how magneto-acoustic waves propagate in sunspot magnetic regions, revealing the nature of observed helioseismology signals and validating the modeling approaches.

Contribution

It provides a detailed theoretical analysis of MHD wave propagation in sunspots, linking wave types to helioseismology observations and validating the eikonal approximation.

Findings

Observed signals correspond to fast MHD waves

Slow MHD waves produce undetected patterns

Numerical results agree with eikonal approximation

Abstract

We use 2D numerical simulations and eikonal approximation, to study properties of MHD waves traveling below the solar surface through the magnetic structure of sunspots. We consider a series of magnetostatic models of sunspots of different magnetic field strengths, from 10 Mm below the photosphere to the low chromosphere. The purpose of these studies is to quantify the effect of the magnetic field on local helioseismology measurements by modeling waves excited by sub-photospheric sources. Time-distance propagation diagrams and wave travel times are calculated for models of various field strength and compared to the non-magnetic case. The results clearly indicate that the observed time-distance helioseismology signals in sunspot regions correspond to fast MHD waves. The slow MHD waves form a distinctly different pattern in the time-distance diagram, which has not been detected in observations. The numerical results are in good agreement with the solution in the short-wavelength (eikonal) approximation, providing its validation. The frequency dependence of the travel times is in a good qualitative agreement with observations.