Speaker
Description
We study the conditions of the solar corona with respect to the occurrence of confined and eruptive (CME-associated) large flares. We model the coronal evolution around 231 large flares observed during solar cycle 24. Based on nonlinear force-free magnetic field extrapolations, we approximate the coronal energy and helicity budgets of the flares' source regions. In particular, we study the characteristics of the pre- and post-flare time evolution of magnetic-field related quantities, including the free magnetic energy and magnetic helicity. We find that during the 24 hours leading to a major flare, the total magnetic energy and unsigned magnetic flux evolve closely with respect to each other -- irrespective of the flare type (confined or eruptive). Prior to confined flares, the free magnetic energy evolves in a way that exhibits more of a similarity with the photospheric unsigned flux than the helicity of the current-carrying field, while the opposite is observed prior to eruptive flares. The coronal energy and helicity budgets return to preflare levels within six to twelve hours or more, serving as a partial explanation for the rare observation of successive eruptive major flares within a time frame of a few hours.