Conversion and Smoothing of MHD Shocks in Atmospheres with Open and Closed Magnetic Field and Neutral Points

TL;DR

This study investigates how MHD shocks behave and transform in complex solar atmospheric magnetic fields with open, closed, and neutral points, revealing that simplified 1.5D results extend to more realistic 2D geometries.

Contribution

It demonstrates that shock mode conversion and smoothing observed in 1.5D models also occur in complex 2D magnetic field configurations, highlighting the role of neutral points and magnetic topology.

Findings

Fast shocks are attracted to neutral points and produce fine structures.

Shocks passing through the Alfvén-acoustic equipartition surface split into fast and slow components.

Slow components are smoothed during mode conversion.

Abstract

Planar acoustically dominated magneto\-hydro\-dynamic waves are initiated at the high-$\beta$ base of a simulated 2D isothermal stratified atmosphere with potential magnetic field exhibiting both open and closed field regions as well as neutral points. They shock on their way upward toward the Alfv\'en-acoustic equipartition surface $a=c$, where $a$ and $c$ are the Alfv\'en and sound speeds respectively. Expanding on recent 1.5D findings that such shocks mode-convert to fast shocks and slow smoothed waves on passing through $a=c$, we explore the implications for these more complex magnetic geometries. It is found that the 1.5D behaviour carries over to the more complex case, with the fast shocks strongly attracted to neutral points, which are disrupted producing extensive fine structure. It is also observed that shocks moving in the opposite direction, from $a>c$ to $a<c$, split into fast and slow components too, and that again it is the slow component that is smoothed.