Onset Process of Eruptive M6.5 Flare in Active Region 12371

Abstract:

We studied the stability of a three-dimensional (3D) magnetic structure to investigate an initiation of the eruptive M6.5 flare in active region (AR) 12371. In order to understand the onset process of the flare, we first extrapolated the 3D coronal magnetic field in AR 12371 using a nonlinear force-free field (NLFFF) model based on time series of the photospheric vector magnetic fields. We found that the flaring region is composed of the two branches of sheared arcade loops which is a sigmoidal structure seen in EUV images. In the basis of the NLFFFs, we examined the stability analysis for the three representative instabilities: the kink, torus, and double arc instabilities. As the results, the two branches of sheared arcade loops are quite stable against the kink and torus instabilities, but unstable against the double arc instability before the flare occurrence. As a possible process of the eruptive flare, we suggest the following three stages: (1) during the initial phase of the flare, the double arc loops are formed by the sheared arcade loops through the tether-cutting reconnection, (2) the destabilized double arc loops are expanded by the DAI, and (3) finally, the torus instabilities contribute to the full eruption. This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (2018-0-01422, Study on analysis and prediction technique of solar flares).