* Astronomy

Title: On the flare induced seismicity in the active region NOAA 10930 and related enhancement of global waves in the sun
Authors: Brajesh Kumar, P. Venkatakrishnan, Savita Mathur, Sanjiv Kumar Tiwari, R. A. Garcia

A major flare (of class X3.4) occurred on 13 December 2006 in the active region NOAA 10930. The energy released during flares is also known to induce acoustic oscillations in the Sun. Here, we analyse the line-of-sight velocity patterns in this active region during the X3.4 flare using the Dopplergrams obtained by GONG instrument. We have also analysed the disk-integrated velocity observations of the Sun obtained by GOLF instrument onboard SOHO spacecraft as well as full-disk collapsed velocity signals from GONG observations during this flare to study any possible connection between the flare related changes seen in the local and global velocity oscillations in the Sun. We apply wavelet transform to the time series of the localised velocity oscillations as well as the global velocity oscillations in the Sun spanning the flare event. The line-of-sight velocity shows significant enhancement in some localised regions of the penumbra of this active region during the flare. The affected region is seen to be away from the locations of the flare ribbons and the hard X-ray footpoints. The sudden enhancement in this velocity seems to be caused by the Lorentz force driven by the "magnetic jerk" in the localised penumbral region. Application of wavelet analysis to these flare induced localised seismic signals show significant enhancement in the high-frequency domain (5-8 mHz) and a feeble enhancement in the p-mode oscillations (2-5 mHz) during the flare. On the other hand, the wavelet analysis of GOLF velocity data and the full-disk collapsed GONG velocity data spanning the flare event indicate significant post-flare enhancements in the high-frequency global velocity oscillations in the Sun. We find indications of a connection between flare induced localised seismic signals and the excitation of global high-frequency oscillations in the Sun.

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