Global hybrid model of the solar wind interaction with the Venus ionosphere: ion escape processes

Abstract

Comprehensive two-dimensional (2D) global hybrid (particle ions, massless fluid electrons) simulations of the solar wind interaction with the ionosphere of Venus are conducted. We calculate the entire Venus–solar wind interaction region including the ionosphere, ionopause transition layer, magnetosheath, and solar wind regions, by applying boundary-fitted coordinates to the particle-in-cell code. Our model is successful in reproducing several observed features, such as long streamers of ionospheric plasma and detached plasma clouds. In this paper, we investigate the processes in which planetary ions are removed by the solar wind interaction using the comprehensive global hybrid model. While the ion escape process due to the pickup of exospheric particles has been intensively studied by many authors, possible ion loss processes that take place at and below the ionopause, such as viscous process associated with the Kelvin–Helmholtz (K–H) instability, are less well understood. Hence, in this paper, the escape processes are investigated with a particular emphasis placed on the processes occurring at the ionopause. We discuss the relative importance of the escape processes for the case of low solar wind dynamic pressure (unmagnetized ionosphere condition) as well as for the high dynamic pressure case (magnetized ionosphere condition), and show the viscous removal process occurring at the ionopause plays a significant role in the ion escape from Venus. The model also suggests the asymmetrical appearance of “disappearing nightside ionosphere”.