A large-scale flow vortex in the Venus plasma tail and its fluid dynamic interpretation

Abstract

We report on the existence of a large-scale ion flow vortex, a curled tailward flow of solar wind H⁺ (SW H⁺), and ionospheric O⁺ in the Venus plasma tail. The vortex commences at dusk (-Y), driven by a transverse (to the solar wind) aberration flow component. Dusk magnetosheath and ionospheric ions move westward across the nightside into the dawn sector, from where the tailward and lateral flow merges into a tailward-moving vortex. A fluid analysis of the SW H⁺ energy and momentum (E&M) transfer to O⁺ at the terminator, shows that E&M balance (efficiency ≈1) is achieved in the altitude range of 1200-600 km. Below 600 km a westward O⁺ flow, moving along the direction of the atmospheric superrotation, dominates. Conversely, SW H⁺ dominates the high-altitude vortex. The Venus large-scale tail vortex is hardly unique. Other gaseous celestial objects (comets) orbiting the Sun may develop similar tail vortices.