HR: 0800h
AN: SM31C-0570    [Abstracts]
TI: A Parametric Study of the Kelvin - Helmholtz Instability of the Supersonic Magnetopause Flanks
AU: Gnavi, G
EM: ggnavi#arnet.com.ar
AF: Instituto de F\'\i sica del Plasma (CONICET and Universidad de Buenos Aires-FCEyN. Also at Physics Department UBA-FCEyN, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
AU: * Farrugia, C
EM: charlie.farrugia@unh.edu
AF: Space Science Center and Dept. of Physics, University of New Hampshire, College Rd., Durham, NH 03824, United States
AU: Gratton, F
EM: fgratton@arnet.com.ar
AF: Instituto de F\'\i sica del Plasma, CONICET and Universidad de Buenos Aires. Also at Pontificia Universidad Católica Argentina-FCFMeI, Av. Alicia M de Justo, Buenos Aires, 1500, Argentina
AU: Bilbao, L
EM: lbilbao@arnet.com.ar
AF: Instituto de F\'\i sica del Plasma (CONICET and Universidad de Buenos Aires-FCEyN. Also at Physics Department UBA-FCEyN, Ciudad Universitaria, Buenos Aires, C1428EHA, Argentina
AU: Torbert, R
AF: Space Science Center and Dept. of Physics, University of New Hampshire, College Rd., Durham, NH 03824, United States
AB: 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 M_A>1, depending on the distance from the dayside terminator (M and M_A 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 M_A remains somewhat smaller M_A ~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 M_A 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.
DE: 2724 Magnetopause and boundary layers
DE: 2752 MHD waves and instabilities (2149, 6050, 7836)
DE: 2753 Numerical modeling
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting