Effective Polytropic Indices of Anisotropic Planetary Magnetosheath Plasmas with Magnetoacoustic Waves

Magnetosheath models for the planets Earth, Jupiter and Saturn are developed within the frame of the double-adiabatic Chew-Goldberger-Low approximation. It is shown that in all three magnetosheaths slow and fast magnetoacoustic waves are generated, the dispersions of which considerably differ from that of isotropic systems. If slow magnetoacoustic waves exist in the magnetosheaths, then the effective polytropic coefficient of the plasma may be smaller than unity - that means compression of the plasma is accompanied, in the average, by cooling. Such polytropic coefficients are not obtained when fast magnetoacoustic waves are excited.