Oscillatory reconnection and waves driven by merging magnetic flux ropes in solar flares

TL;DR

This study uses 2D MHD simulations to demonstrate that oscillatory reconnection occurs naturally during flux rope merging in solar flares, producing waves that could serve as diagnostics for coronal conditions.

Contribution

It reveals that oscillatory reconnection can happen intrinsically during flux rope coalescence without external drivers, and characterizes the resulting wave phenomena.

Findings

Oscillatory reconnection occurs during flux rope merging.

Radial waves are generated post-reconnection with speeds of 90 km/s and 900 km/s.

Wave properties could diagnose physical parameters in the corona.

Abstract

Oscillatory reconnection is a process that has been suggested to underlie several solar and stellar phenomena, and is likely to play an important role in transient events such as flares. Quasi-periodic pulsations (QPPs) in flare emissions may be a manifestation of oscillatory reconnection, but the underlying mechanisms remain uncertain. In this paper, we present 2D magnetohydrodynamic (MHD) simulations of two current-carrying magnetic flux ropes with an out-of-plane magnetic field undergoing oscillatory reconnection in which the two flux ropes merge into a single flux rope. We find that oscillatory reconnection can occur intrinsically without an external oscillatory driver during flux rope coalescence, which may occur both during large-scale coronal loop interactions and the merging of plasmoids in fragmented current sheets. Furthermore, we demonstrate that radially propagating non-linear waves are produced in the aftermath of flux rope coalescence, due to the post-reconnection oscillations of the merged flux rope. The behaviour of these waves is found to be almost independent of the initial out-of-plane magnetic field. It is estimated that the waves emitted through merging coronal loops and merging plasmoids in loop-top current sheets would have a typical phase speed of 90 km/s and 900 km/s respectively. It is possible that the properties of the waves emitted during flux rope coalescence could be used as a diagnostic tool to determine physical parameters within a coalescing region.