Free Magnetic Energy Changes in AR 8210

Abstract

Fourier local correlation tracking (FLCT) was applied to time series of the normal magnetic field in vector magnetograms of NOAA AR 8210, from 17:13–21:29 UT on 1998 May 1, to derive photospheric flows. These flows, combined with both the observed horizontal magnetic field and an inferred horizontal potential magnetic field, can be used to derive the flux of free magnetic energy across the photosphere. Here, we present the formalism used, as well as a map of the time-averaged free energy flux. Over the time interval covered by the magnetograms, ${\sim} 10^{31}\,$erg of free magnetic energy flowed upward across the photosphere, a significant fraction of the energy typically released in large flares coronal mass ejections (CMEs). A flare and coronal mass ejection began at 22:30 UT. We acknowledge the kind support of AFOSR's MURI program.