Fast Restructuring of The Magnetic Field in the Polarity Inversion Line During M9.3 Solar Flare of 2011 July 30

In this report we analyze energy release near the magnetic field polarity inversion line (PIL) during M9.3 solar flare of July 30, 2011. This solar flare is characterized by very strong photospheric perturbations and generation of intensive helioseismic waves. Our goal is to study magnetic field restructureing in this event using new high-cadence vector HMI (Helioseismic Magnetic Imager) magnetograms with temporal resolution of 135 seconds. Standard 720-seconds HMI vector magnetograms are unable to detect magnetic field variations on time scales of the flare impulsive phase. Data analysis revealed strong and fast variations of the magnetic field structure at the PIL on time scale of 135 seconds. A rapid enhancement of the horizontal magnetic field component was observed in the local area with approximate size of 3.5x7 Mm. We also found the rapid amplification of the total vertical photospheric electric current and the growth of the horizontal gradient of the magnetic field vertical component to values greater than 1 kgGs/Mm. We assumed that magnetic loops have a very low height and, therefore, we observe strong and rapid changes in the photospheric magnetic field near the PIL. Possibly such fast change of the magnetic field structure at the PIL was responsible for strong sunquake observed during this solar flare.