1202.4192 (G. J. D. Petrie)
G. J. D. Petrie
The active region NOAA 11158 produced the first X-class flare of Solar Cycle
24, an X2.2 flare at 01:44 UT on 2011 February 15. Here we analyze SDO/HMI
magnetograms covering a 12-hour interval centered at the time of this flare. We
describe the spatial distributions of the photospheric magnetic changes
associated with this flare, including the abrupt changes in the field vector,
vertical electric current and Lorentz force vector. We also trace these
parameters' temporal evolution. The abrupt magnetic changes were concentrated
near the neutral line and in two neighboring sunspots. Near the neutral line,
the field vectors became more horizontal during the flare and the shear
increased. This was due to an increase in strength of the horizontal field
components near the neutral line, most significant in the horizontal component
parallel to the neutral line but the perpendicular component also increased in
strength. The vertical component did not show a significant, permanent overall
change at the neutral line. The increase in total flux at the neutral line was
accompanied by a compensating flux decrease in the surrounding volume. In both
of the sunspots near the neutral line the azimuthal flux abruptly decreased
during the flare but this change was permanent in only one of the spots. There
was a large, abrupt, downward vertical Lorentz force change during the flare,
consistent with results of past analyses and recent theoretical work. The
horizontal Lorentz force acted in opposite directions on each side of neutral
line, with the two sunspots at each end subject to abrupt torsional forces. The
shearing forces were consistent with a decrease of shear near the neutral line,
whereas the field itself became more sheared as a result of the flux collapsing
towards the neutral line from the surrounding volume.
View original:
http://arxiv.org/abs/1202.4192
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