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

Abstract

Planar acoustically dominated magnetohydrodynamic waves are initiated at the high-β 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 Alfvén-acoustic equipartition surface a = c, where a and c are the Alfvén 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.

Benchmarking Hall-Induced Magnetoacoustic to Alfvén Mode Conversion in the Solar Chromosphere

“…In either case though, it splits into distinct acoustically-dominated (now slow) and magnetically dominated (now fast) components in the overlying low-𝛽 upper chromosphere. In the case of shocks, the resulting slow wave is smoothed and soon ★ E-mail: abbas.raboonik@monash.edu † E-mail: paul.cally@monash.edu re-shocks, but the fast wave remains a shock (Pennicott & Cally 2021). However, the fast wave in the upper chromosphere is strongly reflected by the steep Alfvén speed gradient, or the transition region if it reaches it, and so contributes little directly to the corona (Srivastava et al 2021).…”