Secondary Rayleigh-Taylor type Instabilities in the Reconnection Exhaust Jet as a Mechanism for Supra-Arcade Downflows

TL;DR

This paper uses 3D resistive MHD simulations to propose that secondary Rayleigh-Taylor instabilities in reconnecting current sheets can explain the formation of supra-arcade downflows and spikes observed in solar coronae.

Contribution

It introduces a novel mechanism involving secondary Rayleigh-Taylor instabilities as the origin of SADs and spikes in solar flare regions, supported by simulation and observational comparison.

Findings

Secondary Rayleigh-Taylor instabilities develop in reconnecting current sheets.

These instabilities produce low-density SAD-like structures and high-density spikes.

Simulation results align with observed features of SADs and spikes.

Abstract

Supra-arcade downflows (hereafter referred to as SADs) are low-emission, elongated, finger-like features usually observed in active-region coronae above post-eruption flare arcades. Observations exhibit downward moving SADs intertwined with bright upward moving spikes. Whereas SADs are dark voids, spikes are brighter, denser structures. Although SADs have been observed for decades, the mechanism of formation of SADs remains an open issue. In our three-dimensional resistive magnetohydrodynamic simulations, we demonstrate that secondary Rayleigh-Taylor type instabilities develop in the downstream region of a reconnecting current sheet. The instability results in the formation of low-density coherent structures that resemble SADs, and high-density structures that appear to be spike-like. Comparison between the simulation results and observations suggests that secondary Rayleigh-Taylor type instabilities in the exhaust of reconnecting current sheets provide a plausible mechanism for observed SADs and spikes.