A Parametric Study of the Kelvin - Helmholtz Instability of the Supersonic Magnetopause Flanks

Details A Parametric Study of the Kelvin - Helmholtz Instability of the Supersonic Magnetopause Flanks A Parametric Study of the Kelvin - Helmholtz Instability of the Supersonic Magnetopause Flanks

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm31c0570g&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM31C-0570

Physics

2724 Magnetopause And Boundary Layers, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2753 Numerical Modeling

Scientific paper

Compressibility has a strong influence on the stability of velocity shear layers when the difference of velocity Δ V across the flow becomes supersonic. The flanks of the Earth's magnetopause (MP) are normally supersonic M>1, and super-Alfvenic MA>1, depending on the distance from the dayside terminator (M and MA are the sonic and Alfvén Mach numbers, respectively, of the magnetosheath plasma). The stability of MHD supersonic flows depends, also on several features, such as the finite thickness Δ of the boundary layer, the relative orientation of velocity and magnetic fields, the density jump across the boundary, the magnetic shear angle. We analyze the MHD stability of a set of representative flank sites modeled after data from spacecraft crossings of the MP under a variety of interplanetary conditions, complementing these with extrapolations of likely conditions upstream, and downstream of the crossing site. Under northward IMF conditions, there are solar wind regimes such that the near, but already supersonic, flank of the MP may be locally stable. Stability is possible, e.g., when M becomes larger than ~ 1.2 - 1.4 while MA remains somewhat smaller MA ~eq 1.2, and there is magnetic shear between the geomagnetic and the interplanetary magnetic fields. Solar winds favorable to local stability of the boundary layer are cold, not-too-dense plasmas, with strong magnetic fields, so that MA is smaller, while M is larger, than normal values of the magnetosheath flow. A gap between dayside and tail amplifying regions of KH disturbances over the MP may exist when the above conditions are realized.

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