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Paper: Direct Observations of Acoustic Waves Excited by Solar Flares and their Propagation in Sunspot Regions
Volume: 354, Solar MHD Theory and Observations: A High Spatial Resolution Perspective
Page: 154
Authors: Kosovichev, A.G.
Abstract: I present new results from SOHO-MDI of direct observations and analysis of “sunquakes”, seismic acoustic waves excited by solar flares and propagating below the surface through surrounding sunspot regions. The main results are the following: the sources of the seismic waves are associated with hydrodynamic response of the solar atmosphere to high-energy electrons (‘thick-target’ model); the seismic sources are identified in MDI Dopplergrams as compact regions of strong Doppler shift during the flare impulsive phase; the seismic sources are close to the sources of hard X-ray emission and located in flare ribbons; the expanding waves are often anisotropic and non-circular reflecting the properties of the hydrodynamic impact controlled by magnetic field topology in the energy-release regions and subphotospheric condition; the waves have periods of three – five minutes and are best observed about 20 minutes after the impulsive phase; the fronts of the sunquake waves propagating through surrounding sunspots do not show significant distortion and decay, thus giving no evidence for mode conversion in magnetic fields; time-distance diagrams of the seismic waves show only small deviations caused by sunspots in the travel times from the quiet Sun data, which are consistent with the standard travel time measurements from cross-covariance functions. The direct observations of acoustic waves excited by flares open new perspectives for high-resolution helioseismic diagnostics of sunspots and understanding the hydrodynamic processes in solar flares.
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