Numerical simulation of dark lanes in post-flare supra-arcade

TL;DR

This paper uses numerical MHD simulations to model dark voids in post-flare supra-arcades, reproducing observed phenomena and revealing their formation through shock interactions and plasma vacuum creation.

Contribution

It is the first to numerically reproduce dark voids in post-flare supra-arcades and explains their formation via shock interactions and plasma vacuums.

Findings

Dark voids are plasma vacuums caused by shock interactions.

Simulations match observed phase speeds and periods of dark tracks.

Shock bouncing and interference generate the void structures.

Abstract

We integrate the MHD ideal equations to simulate dark void sunwardly moving structures in post--flare supra--arcades. We study the onset and evolution of the internal plasma instability to compare with observations and to gain insight into physical processes and characteristic parameters of these phenomena. The numerical approach uses a finite-volume Harten-Yee TVD scheme to integrate the 1D1/2 MHD equations specially designed to capture supersonic flow discontinuities. The integration is performed in both directions, the sunward radial one and the transverse to the magnetic field. For the first time, we numerically reproduce observational dark voids described in Verwichte et al. (2005). We show that the dark tracks are plasma vacuums generated by the bouncing and interfering of shocks and expansion waves, upstream an initial slow magnetoacoustic shock produced by a localized deposition of energy modeled with a pressure perturbation. The same pressure perturbation produces a transverse to the field or perpendicular magnetic shock giving rise to nonlinear waves that compose the kink--like plasma void structures, with the same functional sunward decreasing phase speed and constancy with height of the period, as those determined by the observations.