Quasi-periodic oscillations in flares and coronal mass ejections associated with magnetic reconnection

TL;DR

This paper investigates the origin of quasi-periodic oscillations in solar flares and CMEs through 2D MHD simulations, revealing how magnetic reconnection dynamics and Lundquist number influence oscillation behavior and turbulence.

Contribution

It introduces a new mechanism linking magnetic reconnection and oscillations in eruptive solar phenomena, supported by numerical simulations across different Lundquist numbers.

Findings

Oscillations occur at moderate and high Lundquist numbers.

Turbulence and plasmoid formation are linked to high Lundquist numbers.

Reconnection jets induce shocks and back-flows causing oscillations.

Abstract

We propose a mechanism for quasi-periodic oscillations of both coronal mass ejections (CMEs) and flare loops as related to magnetic reconnection in eruptive solar flares. We perform two-dimensional numerical MHD simulations of magnetic flux rope eruption, with three different values of the global Lundquist number. In the low Lundquist number run, no oscillatory behavior is found. In the moderate Lunquist number run, on the other hand, quasi-periodic oscillations are excited both at the bottom of the flux rope and at the flare loop-top. In the high Lundquist number run, quasi-periodic oscillations are also excited; in the meanwhile, the dynamics become turbulent due to the formation of multiple plasmoids in the reconnection current sheet. In high and moderate Lundquist number runs, thin reconnection jet collide with the flux rope bottom or flare loop-top and dig them deeply. Steep oblique shocks are formed as termination shocks where reconnection jet is bent (rather than decelerated) in horizontal direction, resulting in supersonic back-flows. The structure becomes unstable, and quasi-periodic oscillation of supersonic back-flows appear at locally confined high-beta region at both the flux rope bottom and flare loop-top. We compare the observational characteristics of quasi-periodic oscillations in erupting flux ropes, post-CME current sheets, flare ribbons and light curves, with corresponding dynamical structures found in our simulation.