Shear driven waves in the induced magnetosphere of Mars: Parameter dependence

Abstract

Low frequency oscillations in the plasma in the induced magnetosphere of Mars were recently measured by the Mars Express spacecraft. Velocity shear was observed, and the plasma was shown to be Kelvin-Helmholtz unstable. In this paper we examine the effects on the frequency and growth rate of the instability when the parameters are varied around the observed values. It is found that if the velocity shear is increased by decreasing the velocity on the low velocity side, i.e. close to the planet, the growth rate increases, while a frequency consistent with the observations can be maintained. When finite Larmor radius effects are included, the growth rate depends on the direction of the vorticity and in the maximum case it is seen to increase substantially, up to a factor of 50, for narrow shear layers. This does also increase the frequency of the oscillations to a large extent.