Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh21c..05w&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH21C-05
Astronomy and Astrophysics
Astrophysics
[7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7529] Solar Physics, Astrophysics, And Astronomy / Photosphere, [7924] Space Weather / Forecasting
Scientific paper
We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking (FLCT) and Differential Affine Velocity Estimator (DAVE) methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96-minute cadence and ~2'' pixels, from 46 active regions (ARs) from 1996-1998 over the time interval t_45 when each AR was within 45 degrees of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, B_R; 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, S_R, equal to the sum of (u B_R^2) over a magnetogram. Several quantities derived from B_R were also computed, including: total unsigned flux; a measure of the amount of unsigned flux near strong-field polarity inversion lines (SPILs), R; and the sum of B_R^2 over each magnetogram. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both t_45 and shorter time windows, of 6 and 24 hours. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during t_45. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S_R, 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 variations in average flare flux.
Fisher George H.
Li Yadong
Schuck Peter W.
Welsch Brian Thomas
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