Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare

TL;DR

This study provides direct spectroscopic and imaging evidence of magnetic reconnection in the solar chromosphere, leading to a microflare, with observed plasma flows and twisted magnetic field structures.

Contribution

It presents the first detailed observations of chromospheric magnetic reconnection associated with a microflare, including plasma flows and flux rope instability evidence.

Findings

Chromospheric line profiles show significant blueshifted and redshifted components during the flare.

Upflows and downflows reach velocities of ±70-80 km/s, comparable to local Alfvén speed.

Twisted magnetic flux rope structures are identified at low altitudes, indicating flux rope instability as a trigger.

Abstract

Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of $\pm$(70--80) km s$^{-1}$, comparable with the local Alfv\'{e}n speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He I 10830 \r{A} images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.