Revealing the nature of magnetic shadows with numerical 3D-MHD simulations

TL;DR

This study uses 3D magnetohydrodynamic simulations to explore how magneto-acoustic waves interact with solar magnetic network elements, revealing the origin of magnetic shadows as a result of wave mode conversion.

Contribution

It demonstrates that magnetic shadows are caused by mode conversion of waves near magnetic network elements, using detailed numerical simulations of wave propagation in a structured magnetic solar atmosphere.

Findings

Magnetic shadows are linked to mode conversion processes.

Power maps show signatures of three different wave modes.

Magnetic shadows appear as suppressed power regions around network elements.

Abstract

We investigate the interaction of magneto-acoustic waves with magnetic network elements with the aim of finding possible signatures of the magnetic shadow phenomenon in the vicinity of network elements. We carried out three-dimensional numerical simulations of magneto-acoustic wave propagation in a model solar atmosphere that is threaded by a complexly structured magnetic field, resembling that of a typical magnetic network element and of internetwork regions. High-frequency waves of 10 mHz are excited at the bottom of the simulation domain. On their way through the upper convection zone and through the photosphere and the chromosphere they become perturbed, refracted, and converted into different mode types. We applied a standard Fourier analysis to produce oscillatory power-maps of the line-of-sight velocity. In the power maps of the upper photosphere and the lower chromosphere, we clearly see the magnetic shadow: a seam of suppressed power surrounding the magnetic network elements. We demonstrate that this shadow is linked to the mode conversion process and that power maps at these height levels show the signature of three different magneto-acoustic wave modes.