Model of superthermal ions in the postshock flow field at Venus

[摘要] 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 $vec {m E} imes vec {m B}$ 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.)

[发布机构] Rice University

[效力级别] physics