EVOLUTION OF OPTICAL PENUMBRAL AND SHEAR FLOWS ASSOCIATED WITH THE X3.4 FLARE OF 2006 DECEMBER 13

Abstract

The rapid and irreversible decay of penumbrae related to X-class flares has been found in a number of studies. Since the optical penumbral flows are closely associated with the morphology of sunspot penumbra, we use state-of-the-art Hinode data to track penumbral flows in flaring active regions as well as shear flows close to the flaring neutral line. This paper concentrates on AR 10930 around the time of an X3.4 flare on 2006 December 13. We utilize the seeing-free solar optical telescope G-band data as a tracer to obtain the horizontal component of the penumbral and shear flows by local correlation tracking, and Stokes-V data to register positive and negative magnetic elements along the magnetic neutral line. We find that: (1) an obvious penumbral decay appears in this active region intimately associated with the X3.4 flare; (2) the mean magnitude of the horizontal speeds of the penumbral flows within the penumbral decay areas temporally and spatially varies from 0.6 to 1.1 km s−1; (3) the penumbral flow decreases before the flare eruption in two of the four penumbral decay areas; (4) the mean shear flows along the magnetic neutral line of this δ-sunspot started to decrease before the flare and continue to decrease for another hour after the flare. The magnitude of this flow apparently dropped from 0.6 to 0.3 km s−1. We propose that the decays of the penumbra and the penumbral flow are related to the magnetic rearrangement involved in the coronal mass ejection/flare events.