2026 PDG seminars

Solar flares as electric circuits detected in multi-wavelength  observations and sunquakes: Seismic responses in the solar interior 

We survey the sunquakes observed so far in cycles 23-25 including the first sunquake with a double bounce or doble ridge in time-distance diagram. We derive the key properties of sunquakes required to explain from the point of view of physical processes in flaring atmospheres and their effects on the  generation of acoustic waves in the solar interior. We explore the outcomes of the hydrodynamic responses of flaring atmospheres to injection of energetic particle, generation of high density shocks traveling towards the solar interior, and the conditions (speed, depth, timing, frequencies) of the generation by them of acoustic waves during propagation in the interior beneath flaring atmospheres. We present first a theory of acoustic waves generated by a point source in stratified plasma and evaluate analytical parametric solutions for a monochromatic source derived for plane-parallel polytrope model of the solar interior. The solution would be used to gain insights into the properties of the generated wavefront as a function of the excitation frequency of acoustic waves and depth of their formation. Then we also consider a varying pressure perturbation, or dense  shock, moving into the solar interior with a supersonic speed. The moving supersonic sources will be shown to excite acoustic waves with a geometry of the generated wavefront constrained by the source depth and its Mach number. The results are discussed in relation to flare simulated for the semiempirical models of the solar interior (Christiansen-Dalsgaard et al, 2003, 2016) and examples of generated acoustic waves in the interior will be presented. The directivity of generated acoustic waves and observational conditions will be also discussed and linked to physical processes in the flaring atmospheres. The simulations results will be compared with some observation of sunquakes.