Abrupt Longitudinal Magnetic Field Changes in Flaring Active Regions

摘要: We characterize the changes in longitudinal photospheric magnetic field during 38 X-class and 39 M-class flares within 65° of disk center using 1 minute GONG magnetograms. In all 77 cases, we identify at least one site flaring active region where clear, permanent, stepwise occurred. The median duration was about 15 minutes approximately equal for flares. absolute values ranged from detection limit ~10 G to as high ~450 two exceptional cases. value 69 G. Field were significantly stronger than limb disk-center Longitudinal less 100 tended decrease strengths, both close limb, while greater showed no such pattern. Likewise, flux strengths Flux changes, particularly net near center, correlated better local with GOES peak X-ray flux. strongest occurred observed limb. estimate change Lorentz force associated each flare find that this is large enough some cases power seismic waves. decreases would likely outnumber increases parts solar our observations, if tilts increase predicted by Hudson et al.