PLASMA TRANSPORT IN THE TOPSIDE VENUS IONOSPHERE R.w.scHuNK

Abeiraet-We have studied the extent to which certain transport processes affect ion composition and heat flow in the daytime, topside Venus ionosphere. Particular attention is given to the conditions that prevailed during the Mariner 5 measurements, at which time the topside Venus ionosphere appeared to be in a state of diffusive equilibrium. We have found that the ion composition is sensitive to the ion temperature, the ion temperature gradient, and to reiative drifts between the ion species of a few m/set. The electron density, on the other hand, is very insensitive to these parameters. As a consequence, ionospheric models of the topside Venus ionosphere are not likely to yield definitive information about the ion composition, the thermal structure or the flow conditions, since at present only electron density profiles are available for testing model predictions. We have also found that a relative drift between the ion species of a few m/see induces an ion heat flow that is equivalent to a 1 K/km temperature gradient. This induced heat flow could influence the energy balance in the topside Venus ionosphere.