SPRG Seminars
March 2, 2010:
" A New Look at the Initiation of Solar Flares "
Dr. Haimin Wang, New Jersey Institute of Technology
Solar flares have been understood as the result of magnetic reconnection in solar corona. Therefore, most flare models assume that the photospheric magnetic fields are anchored, should not have rapid/irreversible changes associated with flares. Recently, it brings us the attention of a paper by Hudson, Fisher and Welsch (2008, ASP, 383, 221), who quantitatively assessed the back reaction on the photosphere and solar interior by the coronal field evolution required to release flare energy. They predicted that after flares, the photospheric magnetic fields turn to more horizontal. We summarize our studies in a number of papers that described changes of magnetic fields associated with flares.
For the events that vector magnetograms are available, we always find a rapid increase of transverse magnetic fields near the magnetic neutral line associated with large flares. This is also related to an earlier study that the reduction of magnetic energy and the consequent reduction of the upward magnetic pressure would inevitably result in the contraction of the overlying field to achieve a new force balance (Hudson, 2000, ApJL, 531, L75). We will present observational evidences of this "implosion" concept in the impulsive phase of flares. Finally, we discuss possible relationship between the rapid changes of photospheric magnetic fields and the excitation of seismic waves--so called "sunquake" (Kosovichev and Zharkova, 1998, Nature, 393, 317).