Abstract
Abstract. We study the solar wind induced oxygen ion escape from Venus' upper atmosphere and the Venus Express observations of the Venus-solar wind interaction by the HYB-Venus hybrid simulation code. We compare the simulation to the magnetic field and ion observations during an orbit of nominal upstream conditions. Further, we study the response of the induced magnetosphere to the emission of planetary ions. The hybrid simulation is found to be able to reproduce the main observed regions of the Venusian plasma environment: the bow shock (both perpendicular and parallel regions), the magnetic barrier, the central tail current sheet, the magnetic tail lobes, the magnetosheath and the planetary wake. The simulation is found to best fit the observations when the planetary \\oxy~escape rate is in the range from 3×1024 s−1 to 1.5×1025 s−1. This range was also found to be a limit for a test particle-like behaviour of the planetary ions: the higher escape rates manifest themselves in a different global configuration of the Venusian induced magnetosphere.
Highlights
The unmagnetized Venus planet has a solar wind interaction very different from the Earth
The Venus Solar Electric (VSE) y-axis is directed along the perpendicular component of the interplanetary magnetic field (IMF) to the x-axis and, the −V SW × BIMF electric field is along the z-axis
In the comparison between the observations and the simulation we identified the perpendicular and parallel bow shocks, the magnetosheath, the magnetic barrier, the central tail current sheet and the magnetic lobe with negative Bx polarity
Summary
The unmagnetized Venus planet has a solar wind interaction very different from the Earth. The high altitude planetary ions are accelerated by the electric and magnetic fields related to the solar wind flow and the Venus’ induced magnetosphere (see, for example, Luhmann et al, 2006, and references therein) These acceleration processes result in a non-thermal escape of the planetary atmosphere. An increase in the EUV radiation modifies the upper atmosphere and enhances the ionization of the exospheric neutral densities This means that more ions are produced and are available for the solar wind induced escape. In this work we compare our Venus hybrid simulation (HYB-Venus) to the VEX particle and magnetic observations and study how the Venus’ plasma environment and the oxygen ion escape change with a wide range of different planetary O+ emission rates. At the end we discuss the results and summarize our findings (Sects. 5 and 6)
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