Probing Current Sheet Instabilities from Flare Ribbon Dynamics

TL;DR

This study uses high-cadence observations of solar flare ribbons to investigate current sheet instabilities, revealing evidence of tearing-mode instability and plasma turbulence during a small solar flare.

Contribution

It provides new observational evidence linking flare ribbon dynamics to current sheet instabilities, especially tearing mode, and turbulence in solar flares.

Findings

Evidence of tearing-mode instability triggering cascade.

Growth of spatial scales correlates with non-thermal velocities.

Power spectrum indicates plasma turbulence.

Abstract

The presence of current sheet instabilities, such as the tearing mode instability, are needed to account for the observed rate of energy release in solar flares. Insights into these current sheet dynamics can be revealed by the behaviour of flare ribbon substructure, as magnetic reconnection accelerates particles down newly reconnected field lines into the chromosphere to mark the flare footpoints. Behaviour in the ribbons can therefore be used to probe processes occurring in the current sheet. In this study, we use high-cadence (1.7 s) IRIS Slit Jaw Imager observations to probe for the growth and evolution of key spatial scales along the flare ribbons - resulting from dynamics across the current sheet of a small solar flare on December 6th 2016. Combining analysis of spatial scale growth with Si IV non-thermal velocities, we piece together a timeline of flare onset for this confined event, and provide evidence of the tearing-mode instability triggering a cascade and inverse cascade towards a power spectrum consistent with plasma turbulence.