Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm41b1875z&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM41B-1875
Physics
Plasma Physics
[2780] Magnetospheric Physics / Solar Wind Interactions With Unmagnetized Bodies, [7836] Space Plasma Physics / Mhd Waves And Instabilities
Scientific paper
The solar wind flow around the ionospheres of unmagnetized planets induces various processes at the boundary layer between the solar wind and ionospheric plasma. In principal, such a flow configuration is thought to be unstable with regard to the Kelvin-Helmholtz instability. Observations of Pioneer Venus Orbiter gave rise to the idea that this instability might lead to the formation of so-called plasma clouds, which consist of ionospheric particles and thus could contribute to the planetary loss. Recently, the magnetometer of Venus Express observed vortices in the magnetic field, giving again rise to the question of the origin of such structures. We present a numerical study of the 2D Kelvin-Helmholtz instability and its vortices, where an initial plasma configuration appropriate for the situation around unmagnetized planets is assumed. We solve the set of ideal MHD equations numerically with the TVD Lax-Friedrichs algorithm. Our density profile is such that the mass density increases toward the lower plasma layer (i.e. the ionosphere). A dense ionosphere leads to smaller growth rates of the instability and thus has a stabilizing effect for the boundary layer. Nevertheless, we find that vortices are able to develop at the boundary layer for most of the cases considered in this investigation. Moreover, we include source terms in the equations, enabling us to study the influence of different conditions (e.g. gravity). Finally, we discuss the role of the instability for the loss of ionospheric particles, thought to be able to escape through plasma clouds possibly generated by the Kelvin-Helmholtz vortices.
Amerstorfer U. V.
Biernat Helfried K.
Zellinger Michael
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