ON THE INSTABILITY AND ENERGY FLUX OF LOWER-HYBRID WAVES IN THE VENUSPLASMA MANTLE

Waves generated near the lower hybrid resonance frequency by the modif ied two stream instability have been invoked as a possible source of e nergy flux into the top-side ionosphere of Venus. These waves are obse rved above the ionopause in a region known as the plasma mantle. The p lasma within the mantle appears to be a mixture of magnetosheath rand ionospheric plasmas. Since the magnetosheath electrons and ions have t emperatures of several tens of eV, any instability analysis of the mod ified two stream instability requires the inclusion of finite electron and ion temperatures. Finite temperature effects are likely to reduce the growth rate of the instability. Furthermore, the lower hybrid wav es are only quasi-electrostatic, and the energy flux of the waves is m ainly carried by parallel Poynting flux. The magnetic field in the man tle is draped over the ionopause. Lower hybrid waves therefore cannot transport any significant wave energy to lower altitudes, and so do no t act as a source of additional heat to the topside ionosphere.