Magnetohydrodynamic simulation of magnetic null-point reconnections in NOAA AR12192 initiated with an extrapolated non-force-free-field

TL;DR

This study uses magnetohydrodynamic simulations initialized with a non-force-free magnetic field to investigate magnetic reconnections near a null point in NOAA AR12192, explaining observed flare ribbons without flux ropes.

Contribution

It introduces a novel simulation approach using an extrapolated non-force-free magnetic field to model 3D null-point reconnections in solar flares.

Findings

Reconnection occurs near the null point with X-type configuration.

Slipping reconnections are observed at quasi-separatrix layers.

The flare is confined with no flux rope involved.

Abstract

Magnetohydrodynamics of the solar corona is simulated numerically. The simulation is initialized with an extrapolated non-force-free magnetic field using the vector magnetogram of the active region (AR) NOAA 12192 obtained on the solar photosphere. Particularly, we focus on the magnetic reconnections occurring close to a magnetic null-point that resulted in appearance of circular chromospheric flare ribbons on October 24, 2014 around 21:21 UT, after peak of an X3.1 flare. The extrapolated field lines show the presence of the three-dimensional (3D) null near one of the polarity inversion lines---where the flare was observed. In the subsequent numerical simulation, we find magnetic reconnections occurring near the null point, where the magnetic field lines from the fan-plane of the 3D null form a X-type configuration with underlying arcade field lines. The footpoints of the dome-shaped field lines, inherent to the 3D null, show high gradients of the squashing factor. We find slipping reconnections at these quasi-separatrix layers, which are co-located with the post-flare circular brightening observed at the chromospheric heights. This demonstrates the viability of the initial non-force-free field along with the dynamics it initiates. Moreover, the initial field and its simulated evolution is found to be devoid of any flux rope, which is in congruence with the confined nature of the flare.