Evolution of Magnetic Fields Associated with Flares and CMEs

This talk reviews recent progress on the study of relationship between evolution of solar magnetic fields and eruptive events such as flares and Coronal Mass Ejections. There are two different time scales of field evolution: (1) longer term in the scale of days, and (2) rapid changes in the time scale of minutes to one hour. The longer term evolution such as magnetic flux emergence and shear motions are well known to play important roles in the energy buildup and triggering of flares. Recent BBSO and MDI magnetograph observations demonstrate more and more evidences of rapid changes of photospheric magnetic fields associated with the core regions of flares and CMEs. We concentrate on the two aspects of such rapid changes: (1) We observed rapid increases of transverse field strength and magnetic shear in flaring neutral line associated with flare. (2) We found that in more than 40 events, part of the penumbral segments in the outer δ spot structure decay rapidly after major flares; meanwhile, the neighboring umbral cores and/or inner penumbral regions become darker. Above changes typically take place in about 10 minutes to one hour and are permanent. In this review, I will also compare several well established flare/CME models that can explain different aspects of our observational results.