Relationship Between Sunspot Rotation and a Major Solar Eruption on 12 July 2012

We present an analysis of Solar Dynamics Observatory (SDO) observations of an X1.4 class flare on 12 July 2012 (SOL2012-07-12T15:37L082C105), which was associated with a pronounced sunspot rotation in the associated active region. Based on the magnetograms taken with the Helioseismic and Magnetic Imager (HMI) on the SDO, we measured the rotational speed of the sunspot. We also used a technique, called the differential affine velocity estimator for vector magnetograms (DAVE4VM), to determine the horizontal velocities and the magnetic helicity flux transport. The helicity flux rate due to shearing motion changed sign after the onset of the eruption. A high correlation between the sunspot rotation speed and the change in the total accumulated helicity was found. We also calculated the net fluxes of the respective magnetic polarities and the net vertical currents. The net current in the region of interest showed a synchronous change with the sunspot rotation rate. The magnetic configurations of the sigmoid filament in the active region and the associated possible interaction between different structures were further investigated by means of a nonlinear force-free field extrapolation. We identified a possible magnetic reconnection region from the three-dimensional magnetic fields and its association with EUV structures. These results suggest that the major eruption of this active region was connected with the sunspot rotation.