Recurrent flares in active region NOAA 11283

Context. Flares and coronal mass ejections (CMEs) are solar phenomena that are not yet fully understood. Several investigations havebeen performed to single out their related physical parameters that can be used as indices of the magnetic complexity leading to theiroccurrence.Aims. In order to shed light on the occurrence of recurrent flares and subsequent associated CMEs, we studied the active regionNOAA 11283 where recurrent M and X GOES-class flares and CMEs occurred.Methods. We use vector magnetograms taken by HMI/SDO to calculate the horizontal velocity fields of the photospheric magneticstructures, the shear and the dip angles of the magnetic field, the magnetic helicity flux distribution, and the Poynting fluxes acrossthe photosphere due to the emergence and the shearing of the magnetic field.Results. Although we do not observe consistent emerging magnetic flux 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 angleshave high values along the main polarity inversion line (PIL) before and after all the events. We also note that before the main flareof X2.1 GOES class, the shearing motions seem to inject a more significant energy than the energy injected by the emergence of themagnetic field.Conclusions. We conclude that the very long duration (about 4 days) of the horizontal displacement of the main photospheric magneticstructures along the PIL has a primary role in the energy release during the recurrent flares. This peculiar horizontal velocity fieldalso contributes to the monotonic injection of magnetic helicity into the corona. This process, coupled with the high shear and dipangles along the main PIL, appears to be responsible for the consecutive events of loss of equilibrium leading to the recurrent flaresand CMEs.