Laurent Beauregard, Meetu Verma, Carsten Denker
Horizontal proper motions were measured with local correlation tracking (LCT)
techniques in active region NOAA 11158 on 2011 February 15 at a time when a
major (X2.2) solar flare occurred. The measurements are based on continuum
images and magnetograms of the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory. The observed shear flows along the polarity
inversion line were rather weak (a few 100 m/s). The counter-streaming region
shifted toward the north after the flare. A small circular area with flow
speeds of up to 1.2 km/s appeared after the flare near a region of rapid
penumbral decay. The LCT signal in this region was provided by small-scale
photospheric brigthenings, which were associated with fast traveling moving
magnetic features. Umbral strengthening and rapid penumbral decay was observed
after the flare. Both phenomena were closely tied to kernels of white-light
flare emission. The white-light flare only lasted for about 15 min and peaked 4
min earlier than the X-ray flux. In comparison to other major flares, the X2.2
flare in active region NOAA 11158 only produced diminutive photospheric
signatures.
View original:
http://arxiv.org/abs/1201.2800
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