New Observations of Flare-Generated Sunquakes

Solar flares may produce "sunquakes", strong localized compressions in the photosphere, which generate acoustic waves propagating through the Sun's interior. These seismic waves are observed on the solar surface as expanding wave rings. Several strong sunquake events were observed by the Solar and Heliospheric Observatory (SOHO) in 2003-2005, long after the first sunquake detected in 1996. Detailed analysis of these events SOHO and RHESSI space missions reveals new interesting properties of the seismic response to solar flares, such as close association between the hard X-ray flare emission and the hydrodynamic impacts on the solar surface, strong anizotropy of the seismic waves, and their interaction with sunspots. These results are of significant interest for understanding the physics of energy release and transport in solar flares, and for helioseismic diagnostics of flaring active regions. An intriguing question is why the sunquakes have been observed only during the declining phases of the solar activity cycle.