THE MAGNETIC SYSTEMS TRIGGERING THE M6.6 CLASS SOLAR FLARE IN NOAA ACTIVE REGION 11158

Abstract

We report a detailed event analysis on the M6.6-class flare in the active\nregion (AR) NOAA 11158 on 2011 February 13. AR 11158, which consisted of two\nmajor emerging bipoles, showed prominent activities including one X- and\nseveral M-class flares. In order to investigate the magnetic structures related\nto the M6.6 event, particularly the formation process of a flare-triggering\nmagnetic region, we analyzed multiple spacecraft observations and numerical\nresults of a flare simulation. We observed that, in the center of this\nquadrupolar AR, a highly sheared polarity inversion line (PIL) was formed\nthrough proper motions of the major magnetic elements, which built a sheared\ncoronal arcade lying over the PIL. The observations lend support to the\ninterpretation that the target flare was triggered by a localized magnetic\nregion that had an intrusive structure, namely a positive polarity penetrating\ninto a negative counterpart. The geometrical relationship between the sheared\ncoronal arcade and the triggering region was consistent with the theoretical\nflare model based on the previous numerical study. We found that the formation\nof the trigger region was due to a continuous accumulation of the small-scale\nmagnetic patches. A few hours before the flare occurrence, the series of\nemerged/advected patches reconnected with a preexisting fields. Finally, the\nabrupt flare eruption of the M6.6 event started around 17:30 UT. Our analysis\nsuggests that, in a triggering process of a flare activity, all magnetic\nsystems of multiple scales, not only the entire AR evolution but also the fine\nmagnetic elements, are altogether involved.\n