In this study, we clarify the triggering process of the X1.0 flare produced in the great active region (AR) NOAA 12192 on 2014 October 24. The AR 12192 had very complicated magnetic structure, which was classified to δ-type sunspot and produced six X-class flares during disk passage. The AR showed complicated shape of the polarity inversion lines (PIL), and the X1.0 flare produced three flare-ribbons in contract to the standard two-ribbon flare. We investigated the triggering process of the X1.0 flare to explain the cause of the complex structure.
We analyzed filter and vector magnetograms and filtergrams of each layer in the solar atmosphere obtained by Hinode/SOT and SDO/HMI, AIA. We superposed contours of the chromospheric emissions on the filter magnetograms, and investigated the correlation between the magnetic structures and the strong emissions in the chromosphere. We also investigated the non-potentiality by measuring the angle between the potential field and the transverse magnetic field in the photosphere. Moreover, we compared the observed features and the coronal magnetic fields extrapolated by the NLFFF method (Inoue+2014) in order to clarify the trigger process of the flare.
As a result, we identified the “flare trigger field” of the X1.0 flare, and found that the triggering process was two-step from the preceding C9.7 to the X1.0 flares. The flare trigger process satisfied one of the two types of flare trigger process proposed by Kusano+2012 using the numerical simulation. We also found the plasma flow that is suggestive of the tether-cutting reconnection proposed by Moore+2001, in AIA 171 Å images. Moreover, we found that the flare trigger field locates slight off of the PIL although the numerical simulation of Kusano+2012 puts the flare trigger field just above the PIL. Therefore, our results give a specific suggestion that the theoretical flare trigger model is applicable even though the small flare trigger field is located off the PIL as long as the topological conditions proposed by Kusano+ are satisfied.