Observations of solar flares with sunquakes by space- and ground-based instruments
reveal essentially different dynamics of seismic events in different flares. Some sunquakes
are found to be closely associated with the locations of hard X-ray (HXR) and whitelight
(WL) emission, while others are located outside either of them. In this article we investigate
possible sources causing a seismic response in a form of hydrodynamic shocks
produced by the injection of mixed (electron plus proton) beams, discuss the velocities of
these shocks, and the depths where they deposit the bulk of their energy and momentum.
The simulation of hydrodynamic shocks in flaring atmospheres induced by electron-rich and
proton-rich beams reveals that the linear depth of the shock termination is shifted beneath
the level of the quiet solar photosphere on a distance from 200 to 5000 km. The parameters
of these atmospheric hydrodynamic shocks are used as initial condition for another hydrodynamic
model developed for acoustic-wave propagation in the solar interior (Zharkov, Mon.
Not. Roy. Astron. Soc. 431, 3414, 2013). The model reveals that the depth of energy and
momentum deposition by the atmospheric shocks strongly affects the propagation velocity
of the acoustic-wave packet in the interior. The locations of the first bounces from the
photosphere of acoustic waves generated in the vicinity of a flare are seen as ripples on the
solar surface, or sunquakes. Mixed proton-dominated beams are found to produce a strong
supersonic shock at depths 200 ? 300 km under the level of the quiet-Sun photosphere and in
this way produce well-observable acoustic waves, while electron-dominated beams create a
slightly supersonic shock propagating down to 5000 km under the photosphere. This shock
can only generate acoustic waves at the top layers beneath the photosphere since the shock
velocity very quickly drops below the local sound speed. The distance 'delta' of the first bounce of the generated acoustic waves is discussed in relation to the minimal phase velocities of
wave packets defined by the acoustic cutoff frequency and the parameters of atmospheric
shock termination beneath the photosphere.
Authors: Zharkova V.V. and Zharkov S.I.
Publication Status: published, Solar Physics journal
Last Modified: 2015-11-20 15:38