Flare Energy Release in the Low Solar Atmosphere: Fine Structuring, Electric Currents and Sunquakes.

Abstract:

Observations of C2.1 flare of August 15, 2011, obtained at NST/BBSO, reveal fine structuring of H-alpha flare ribbons (with a characteristic width ~100 km). Using SDO/HMI vector magnetic field measurements we calculate vertical electric currents and discuss their role in the flare energy release. We argue that the observed fine structuring of the flare ribbons can be associated with dissipation of electric currents in the partially ionized chromospheric plasma. We also discuss the role of electric currents in two flares with sunquakes: C7.0 flare of Febrary 17, 2013, and M9.2 flare of July 30, 2011. We find that the observed sunquake impacts do not spatially correlate with the strongest HXR emission sources but coincide with the intensive electric currents. These observations suggest that the primary energy release can be connected with rapid dissipation of electric currents in the low atmosphere. We also conclude that the fine structuring of the electric currents may play a very important role, as it leads to enhanced and fast magnetic energy release, especially in the case of turbulent and ambipolar resistivity which can take place in the low solar atmosphere.