On the seismic emission in sunspots associated with Lorentz force changes accompanying major solar flares

Abstract

ABSTRACT Solar flares are known to generate seismic waves in the Sun. We present a detailed analysis of seismic emission in sunspots accompanying M- and X-class solar flares. For this purpose, we have used high-resolution Dopplergrams and line-of-sight magnetograms at a cadence of 45 s, along with vector magnetograms at a cadence of 135 s obtained from Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory space mission. In order to identify the location of flare ribbons and hard X-ray footpoints, we have also used Hα chromospheric intensity observations obtained from Global Oscillation Network Group instruments and hard X-ray images in 12–25 keV band from the Reuvan Ramaty High Energy Solar Spectroscopic Imager spacecraft. The fast Fourier transform technique is applied to construct the acoustic velocity power map in 2.5–4 mHz band for pre-flare, spanning flare, and post-flare epochs for the identification of seismic emission locations in the sunspots. In the power maps, we have selected only those locations which are away from the flare ribbons and hard X-ray footpoints. These regions are believed to be free from any flare related artefacts in the observational data. We have identified concentrated locations of acoustic power enhancements in sunspots accompanying major flares. Our investigation provides evidence that abrupt changes in the magnetic fields and associated impulsive changes in the Lorentz force could be the driving source for these seismic emissions in the sunspots during solar flares.