WHAT IS THE RELATIONSHIP BETWEEN PHOTOSPHERIC FLOW FIELDS AND SOLAR FLARES?

Abstract

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking and Differential Affine Velocity Estimator methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96 minute cadence and ~2'' pixels, from 46 active regions (ARs) from 1996 to 1998 over the time interval τ45 when each AR was within 45° of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, ; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, . Several quantities derived from were also computed, including: Φ, the total unsigned flux; R, a measure of the unsigned flux near strong-field polarity inversion lines; and . Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both τ45 and shorter time windows of 6 and 24 hr. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during τ45. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, SR , was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are ~0.25, implying no single variable that we considered can explain the majority of variability in average flare flux.