Recurrent flares in active region NOAA 11283^⋆

¹ INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
e-mail: prom@oact.inaf.it
² Dipartimento di Fisica e Astronomia – Sezione Astrofisica, Universitá di Catania, via S. Sofia 78, 95123 Catania, Italy
³ Department of Physics, Universitá di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴ INAF–IAPS Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Rome, Italy
⁵ Dipartimento di Fisica, Universitá della Calabria, 87036 Rende ( CS), Italy
⁶ Dipartimento di Fisica, Universitá and Area di Ricerca in Astrogeofisica, 67100 L’Aquila, Italy
⁷ Department of Physics and Astronomy, King Saud University, 11451 Riyadh, Saudi Arabia
⁸ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
⁹ INAF–Osservatorio Astronomico di Torino, Strada Osservatorio 20, Pino Torinese (TO), Italy
¹⁰ Dipartimento di Fisica e Astronomia, SASS, Universitá degli Studi di Firenze, Largo E. Fermi 2, 50125 Firenze, Italy
¹¹ Istituto Nazionale di Geofisica e Vulcanologia – Sede di Cosenza, 87036 Rende (CS), Italy

Received: 13 February 2015
Accepted: 8 August 2015

Abstract

Context. Flares and coronal mass ejections (CMEs) are solar phenomena that are not yet fully understood. Several investigations have been performed to single out their related physical parameters that can be used as indices of the magnetic complexity leading to their occurrence.

Aims. In order to shed light on the occurrence of recurrent flares and subsequent associated CMEs, we studied the active region NOAA 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 magnetic structures, the shear and the dip angles of the magnetic field, the magnetic helicity flux distribution, and the Poynting fluxes across the 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 angles have high values along the main polarity inversion line (PIL) before and after all the events. We also note that before the main flare of X2.1 GOES class, the shearing motions seem to inject a more significant energy than the energy injected by the emergence of the magnetic field.

Conclusions. We conclude that the very long duration (about 4 days) of the horizontal displacement of the main photospheric magnetic structures along the PIL has a primary role in the energy release during the recurrent flares. This peculiar horizontal velocity field 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 flares and CMEs.