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

Waves generated near the lower hybrid resonance frequency by the modified two stream instability have been invoked as a possible source of energy flux into the top-side ionosphere of Venus. These waves are observed above the ionopause in a region known as the plasma mantle. The plasma within the mantle appears to be a mixture of magnetosheath rand ionospheric plasmas. Since the magnetosheath electrons and ions have temperatures of several tens of eV, any instability analysis of the modified 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 waves are only quasi-electrostatic, and the energy flux of the waves is mainly carried by parallel Poynting flux. The magnetic field in the mantle is draped over the ionopause. Lower hybrid waves therefore cannot transport any significant wave energy to lower altitudes, and so do not act as a source of additional heat to the topside ionosphere.