Current-sheet Oscillations Caused by Kelvin-Helmholtz Instability at the Loop Top of Solar Flares

TL;DR

This study uses high-resolution MHD simulations to reveal that Kelvin-Helmholtz instability causes oscillations in solar flare current sheets, and proposes a new method to measure magnetic fields in these structures.

Contribution

It demonstrates that KHI-induced turbulence excites observable current sheet oscillations and introduces a novel technique for magnetic field measurement in solar flare current sheets.

Findings

KHI excites large-amplitude transverse waves in current sheets.

Oscillations propagate upward with phase speed near local Alfvén speed.

A new method for measuring magnetic field strength in current sheets is proposed.

Abstract

Current sheets (CSs), long stretching structures of magnetic reconnection above solar flare loops, are usually observed to oscillate, their origins, however, are still puzzled at present. Based on a high-resolution 2.5-dimensional MHD simulation of magnetic reconnection, we explore the formation mechanism of the CS oscillations. We find that large-amplitude transverse waves are excited by the Kelvin-Helmholtz instability (KHI) at the highly turbulent cusp-shaped region. The perturbations propagate upward along the CS with a phase speed close to local Alfv\'{e}n speed thus resulting in the CS oscillations we observe. Though the perturbations damp after propagating for a long distance, the CS oscillations are still detectable. In terms of detected CS oscillations, with a combination of differential emission measure technique, we propose a new method for measuring the magnetic field strength of the CSs and its distribution in height.