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Recurrent Coronal Jets Induced by Repetitively Accumulated Electric Currents

Three extreme-ultraviolet (EUV) jets recurred in about one hour on 2010 September 17 in the following magnetic polarity of active region 11106. The EUV jets were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The Helioseismic and Magnetic Imager (HMI) on board SDO measured the vector magnetic field, from which we derive the magnetic flux evolution, the photospheric velocity field, and the vertical electric current evolution. The magnetic configuration before the jets is derived by the nonlinear force-free field (NLFFF) extrapolation. We derive that the jets are above a pair of parasitic magnetic bipoles which are continuously driven by photospheric diverging flows. The interaction drove the build up of electric currents that we indeed observed as elongated patterns at the photospheric level. For the first time, the high temporal cadence of HMI allows to follow the evolution of such small currents. In the jet region, we found that the integrated absolute current peaks repetitively in phase with the 171 A flux evolution. The current build up and its decay are both fast, about 10 minutes each, and the current maximum precedes the 171 A by also about 10 minutes. Then, HMI temporal cadence is marginally fast enough to detect such changes. The photospheric current pattern of the jets is found associated to the quasi-separatrix layers deduced from the magnetic extrapolation. From previous theoretical results, the observed diverging flows are expected to build continuously such currents. We conclude that magnetic reconnection occurs periodically, in the current layer created between the emerging bipoles and the large scale active region field. It induced the observed recurrent coronal jets and the decrease of the vertical electric current magnitude.