Shear driven waves in the induced magnetosphere of Mars: parameter dependence U. V. Amerstorfer1, H. Gunell2, N. V. Erkaev3, and H. K. Biernat1 1Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria 2Department of Physics, West Virginia University, Morgantown, WV 26506-6315, USA 3Institute of Computational Modelling, Russian Academy of Sciences, 660036 Krasnoyarsk-36, Russia
Received: 20 Mar 2009 – Revised: 02 Jun 2009 – Accepted: 03 Jul 2009 – Published: 11 Sep 2009
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.
Citation: Amerstorfer, U. V., Gunell, H., Erkaev, N. V., and Biernat, H. K.: Shear driven waves in the induced magnetosphere of Mars: parameter dependence, Astrophys. Space Sci. Trans., 5, 39-42, doi:10.5194/astra-5-39-2009, 2009.