Giant vortices lead to ion escape from Venus and re-distribution of plasma in the ionosphere

Abstract

[1] The interaction of the solar wind with Venus has a significant influence on the evolution of its atmosphere. Due to the lack of an intrinsic planetary magnetic field, there is direct contact between the fast flowing solar wind and the Venusian ionosphere. This leads to a number of different types of atmospheric escape process. Using Venus Express observations, we show that such contact leads to the formation of global vortices downstream of the Venusian bow shock. These vortices accelerate heavy ionospheric ions such as oxygen, leading to their escape. We argue that these vortices are the result of the Kelvin-Helmholtz instability excited by the shear velocity profile at the boundary between the solar wind and ionospheric plasma. These vortices also help to repopulate the night-side ionosphere during solar minimum, when the ionospheric flow from dav to night is restricted by the lowered ionopause altitude at the terminator. Copyright 2009 by the American Geophysical Union.