Quantifying the Topology and Evolution of a Magnetic Flux Rope Associated with Multi-flare Activities

TL;DR

This study analyzes the magnetic topology and evolution of a magnetic flux rope in solar active region 12017, revealing its role in flare activity and the importance of twist number and QSL structure in flare triggering.

Contribution

It provides a detailed quantitative assessment of the MFR's topology, evolution, and its relation to flare activity using advanced magnetic field extrapolation and analysis methods.

Findings

The MFR is cospatial with the filament and surrounded by a closed QSL.

The QSL structure shrinks as flares occur.

Flares are mainly triggered by kink instability, with twist number being a sensitive indicator.

Abstract

Magnetic flux rope (MFR) plays an important role in solar activities. A quantitative assessment of the topology of an MFR and its evolution is crucial for a better understanding of the relationship between the MFR and the associated activities. In this paper, we investigate the magnetic field of active region 12017 from 2014 March 28 to 29, where 12 flares were triggered by the intermittent eruptions of a filament (either successful or confined). Using the vector magnetic field data from the Helioseismic and Magnetic Imager on board the \textit{Solar Dynamics Observatory}, we calculate the magnetic energy and helicity injection in the active region, and extrapolate the 3D magnetic field with a nonlinear force-free field model. From the extrapolations, we find an MFR that is cospatial with the filament. We further determine the configuration of this MFR by a closed quasi-separatrix layer (QSL) around it. Then, we calculate the twist number and the magnetic helicity for the field lines composing the MFR. The results show that the closed QSL structure surrounding the MFR gets smaller as a consequence of the flare occurrence. We also find that the flares in our sample are mainly triggered by kink instability. Moreover, the twist number varies more sensitively than other parameters to the occurrence of flares.