Velocity and Magnetic Transients Driven by the X2.2 White-light Flare of 2011 February 15 in NOAA 11158

Abstract

The first X-class flare of the current solar cycle 24 occurred in Active Region NOAA 11158 during its central meridian passage on 2011 February 15. This two-ribbon white-light flare was observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. During the peak phase of the flare, we detected magnetic and Doppler velocity (DV) transients appearing near the umbral boundary of the main sunspot. These transients persisted for a few minutes and showed spatial and temporal correspondence with the flare kernels. The observed magnetic polarity at the transients' locations underwent a sign reversal, together with a large enhancement in DVs. We explain this observational phenomenon using the HMI spectral data obtained before, during, and after the flare. These changes were reflected in the maps of the active region in all the Stokes parameters. Association of the transient features with various signatures of the flare and the cause and effects of their appearance are also presented on the basis of present theoretical models.