The analogy between sunquakes and water waves

Abstract

To investigate the seismic waves generated at the surface of the convection zone by a sunquake, the solar convection zone is modeled as an incompressible fluid layer of finite depth which is excited by a pressure pulse just above the solar surface. Solutions for the surface displacement ζ as a function of time are obtained by solving the linearized Euler equations for wave propagation in an inviscid, incompressible fluid. Approximate solutions are derived using the method of stationary phase and formulas are obtained for the position of the wave crests versus time and the decay of the wave amplitude versus distance. Despite the very simple nature of the model, the resulting time–distance relation is found to exhibit the correct order of magnitude when compared to the observations of the flare initiated sunquake of 9 July 1996. However, the water wave model cannot fully explain the observations because, for one thing, the distance in between successive wave crests is greater than that seen in the observations. One may conclude that the sunquake is probably composed primarily of acoustic waves, that is, p modes and not f modes.