Wave coupling at contact discontinuities

The study of wave coupling at a contact discontinuity provides an insight into the propagation characteristics of geomagnetic pulsations in the magnetosphere. Two semi-infinite fluids, described by collisionless double adiabatic equations and separated by a planar interface are considered. The reflection and transmission coefficients are computed. It is found that for density ratio representative of the solar wind - magnetosphere boundary, there is very little energy in the transmitted fast wave but substantial flux in the slow transmitted wave. For gradients characterizing the polar magnetosphere there is considerable transmission for both the fast and slow waves (50% or more). The Alfven wave, which is not coupled to the magnetoacoustic waves, is efficiently transmitted in both the cases. (author)