Browsing by Author "Kramer, Leonard"

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    Model of superthermal ions in the dayside Venus ionosphere
    (1993) Kramer, Leonard; Cloutier, Paul A.
    A model is presented which simulates the behavior of superthermal ions previously reported in the dayside ionosphere of Venus. The model considers effects of E $\times$ B and gradient drifts, charge exchange and collisions with the ambient neutral atmosphere and the possible effects of a wave-particle (anomalous) scattering process. Results indicate that scattering processes are required if superthermal ions are the explanation for the observed "missing pressure" component in the dayside Venus ionosphere. The scattering scale length required to match the "missing pressure" distribution is similar to the scale length previously predicted for growth of a lower hybrid beam instability.
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    Model of superthermal ions in the postshock flow field at Venus
    (1992) Kramer, Leonard; Cloutier, Paul A.
    The role of the superthermal ions in the dayside postshock ionospheric flow field at Venus is investigated in a 2-D model by integrating the equation of motion of a superthermal population of O$\sp+$ test particles and statistically examining their contribution to the altitude variation of number density and horizontal current distribution. The model reveals superthermal ions $\vec {\rm E} \times \vec {\rm B}$ drifting downward and gradient drifting horizontally with attendant currents. Regions of "wrapped up" plasma known as fluxropes and identified previously as resulting from Kelvin-Helmholtz instability in the ionosphere are found to significantly scatter ions and limit the horizontal currents. Monte-Carlo simulation of charge exchange and subsequent neutral-on-neutral collision processes produce a substantial vertical flux of ballistic neutrals with hyperbolic trajectories possibly representing a heretofore unrecognized atmospheric loss mechanism at Venus. Modeled altitude profiles of superthermal density superficially agree with empirical analysis by Stewart (1991) for a "missing" pressure term in the momentum balance requirements. (Abstract shortened with permission of author.)