Flares and Magnetic Non-potentiality of NOAA AR 11158

Song Qiao, qsong@nao.cas.cn, NAOC China
Zhang Jun, NAOC
Yang Shuhong, NAOC
Liu Yang, Stanford University

Abstract
The magnetic non-potentiality is important for us to understand flares and others solar activities in active regions (ARs). Five non-potential parameters, i.e., electric current (Jz), current helicity (Hc), source field (SF), free energy (FE), and angular shear (AS), are calculated in this work to quantify the non-potentiality of NOAA AR 11158. Benefited from high spatial resolution, high cadence, and uninterrupted vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, both the long-term evolution of the AR and the rapid change during flares have been studied. The major results of this work are as follows. (1) AR 11158 is formed from at least 10 emerging flux regions. (2) Three phases are found in the evolution of Jz, Hc, FE, and AS in the AR. (3) The center distant between the positive and the negative Hc systems increases with the development of the AR, and turns into a decrease about 6 hr after the eruption of the first X-class flare in Solar Cycle 24. (4) The increase of AS and Hc around a polarity inversion line and decrease at its outskirts during the flare are identified in the AR. (5) Rapid and prominent increases are found in the variation of Hc during the flares in their initial brightening regions. The recovery of the increases takes 3-4 hr for the two biggest flares, while only takes about 2 hr for the other two smaller flares. (6) An opposite sign area in AS map during the X2.2 flare has an interesting spatial correlation with the source region of a sunquake event. The results confirm that the non-potentiality has an intimate connection with the flare.