Recurrent flares in active region NOAA 11283

Context. Flares and coronal mass ejections (CMEs) are solar phenomena not yet fully understood. Several investigations have been carried out to single out their related physical parameters that can be used as indeces of the magnetic complexity leading to their occurrence. Aims. In order to shed light on the occurrence of recurrent ares and subsequent associated CMEs, we studied the active region NOAA 11283 where recurrent M and X GOES-class ares and CMEs occurred. Methods.We use vector magnetograms taken by HMI/SDO to calculate the horizontal velocity elds of the photospheric magnetic structures, the shear and the dip angles of the magnetic eld, the magnetic helicity ux distribution, and the Poynting uxes across the photosphere due to the emergence and the shearing of the magnetic eld. Results. Although we do not observe consistent emerging magnetic ux through the photosphere during the observation time interval, we detected a monotonic increase of the magnetic helicity accumulated in the corona. We found that both the shear and the dip angles have high values along the main polarity inversion line (PIL) before and after all the events. We also note that before the main are of X2.1 GOES class, the shearing motions seem to inject a more signicant energy in comparison with the energy injected by the emergence of the magnetic eld. Conclusions. We conclude that the very long duration (about 4 days) horizontal displacement of the main photospheric magnetic structures along the PIL has a primary role in the energy release during the recurrent ares. This peculiar horizontal velocity eld also contributes to the monotonic injection of magnetic helicity into the corona. This process, coupled with the high shear and dip angles along the main PIL, appears to be responsible for the consecutive events of loss of equilibrium leading to the recurrent ares and CMEs.