Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm41b1876a&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM41B-1876
Physics
Plasma Physics
[2780] Magnetospheric Physics / Solar Wind Interactions With Unmagnetized Bodies, [7836] Space Plasma Physics / Mhd Waves And Instabilities
Scientific paper
Both observations and theoretical investigations give rise to the assumption that a boundary layer between the solar wind and a planetary ionosphere is unstable with respect to the Kelvin-Helmholtz instability. Moreover, observations indicate a connection between waves on the dayside of the boundary and detached plasma structures (“plasma clouds”) around and downstream of the terminator. Just recently, Venus Express measurements were reported that show vortex structures in the magnetic field. We study the 2D nonlinear Kelvin-Helmholtz instability by numerically integrating the MHD equations, using the TVD Lax-Friedrichs algorithm. We thereby assume initial plasma configurations, which are applicable for unmagnetized planets. A special focus is placed upon the influence of the total pressure, which is the sum of the plasma and magnetic pressures, on the evolution of the Kelvin-Helmholtz instability and vortices. In the case of planetary magnetosheath flow, the total pressure is a decreasing function of the distance from the subsolar point along a streamline, while the velocity shear is an increasing function along the ionopause. For a fixed velocity shear, a decreasing total pressure seems to decrease the growth rate, whereas for a fixed total pressure, an increasing shear increases the growth rate. Thus, the growth rate of the instability should have a maximum at some distance from the subsolar point, which we estimate from our investigations. Apart from the total pressure, a crucial factor for the growth of the instability is the ratio of magnetospheric to ionospheric mass density, and we find a logarithmic-type approximation for the dependence of the growth rate on the density ratio. Finally, we give rough estimations of the loss rates of planetary ionosphere particles, which might be lost through plasma clouds possibly emanating from the vortices.
Amerstorfer U. V.
Biernat Helfried K.
Erkaev Nikolai V.
Zellinger Michael
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