MHD wave propagation from the sub-photosphere to the corona in an arcade-shaped magnetic field with a null point

TL;DR

This study uses 2D numerical simulations to analyze how MHD waves propagate through the solar atmosphere's magnetic structures, revealing mechanisms that allow energy transfer from the sub-photosphere to the corona, especially along vertical flux tubes.

Contribution

It provides detailed insights into wave behavior in complex magnetic topologies with null points, highlighting the role of refraction, conversion, and reflection in energy transport.

Findings

Energy reaches the corona mainly along vertical flux tubes with acoustic nature.

Most magnetic energy remains below the transition region due to refraction and conversion.

High-frequency waves can penetrate to the corona outside flux tubes.

Abstract

The aim of this work is to study the energy transport by means of MHD waves propagating in quiet Sun magnetic topology from layers below the surface to the corona. Upward propagating waves find obstacles, such as the equipartition layer with plasma b=1 and the transition region, and get converted, reflected and refracted. Understanding the mechanisms by which MHD waves can reach the corona can give us information about the solar atmosphere and the magnetic structures. We carry out two-dimensional numerical simulations of wave propagation in a magnetic field structure that consists of two vertical flux tubes separated by an arcade shaped magnetic field. This configuration contains a null point in the corona, that significantly modifies the behaviour of the waves. We describe in detail the wave propagation through the atmosphere under different driving conditions. We also present the spatial distribution of the mean acoustic and magnetic energy fluxes and the spatial distribution of the dominant frequencies in the whole domain. We conclude that the energy reaches the corona preferably along vertical magnetic fields, inside the flux tubes, and it has an acoustic nature. Most of the magnetic energy keeps concentrated below the transition region due to the refraction of the magnetic waves and the continuous conversion of acoustic-like waves into fast magnetic waves in the equipartition layer located in the photosphere. However, part of the magnetic energy reaches the low corona when propagating in the region where the arcades are located, but waves are sent back downwards to the lower atmosphere at the null point surroundings. This phenomenon, together with the reflection and refraction of waves in the TR and the lower turning point, act as a re-feeding of the atmosphere. In the frequency distribution, we find that high frequency waves can reach the corona outside the vertical flux tubes.