ON THE RESPONSE OF EXOSPHERIC TEMPERATURE ON VENUS TO SOLAR-WIND CONDITIONS

Exospheric temperatures (T(ex)) inferred from in-situ measurements of neutral densities by the Pioneer Venus Orbiter have been analyzed to examine any possible dependence on solar wind dynamic pressure (P(sw)). We do not find any linear relationship between P(sw) and T(ex). However, on one occasion when P(sw) was unusually high for a prolonged period, an unmistakable temperature enhancement was observed. Minor enhancements of T(ex) were also observed in a few other cases, with sustained but moderately high P(sw).