Reflection and refraction of hydromagnetk waves at the magnetopause

Reflection and transmission coefficients of MHD waves are obtained at a stable, plane interface which separates two compressible, perfectly conducting media in relative motion to each other. The coefficients are evaluated for representative conditions of the quiettime, near-Earth magnetopause. The transmission coefficient averaged over a hemispherical distribution of incident waves is found to be 1–2 per cent. Yet the magnitude of the energy flux deposited into the magnetosphere in a day averaged over a hemispherical distribution of waves having amplitudes of say 2–3 gamma, is estimated to be of the order 10²² erg. Therefore the energy input of MHD waves must contribute significantly to the energy budget of the magnetosphere. The assumption that the boundary surface is a tangential discontinuity with no curvature limits the present theory to hydromagnetic frequencies higher than about 10^?1 Hz. The ion gyrofrequencies for the models assumed here lie above 2 × 10^?1 Hz. Therefore the present treatment applies to MHD waves near 10^?1 Hz.