HR: 1330h
AN: SM43A-02    [Abstracts]
TI: A Kinetic Interchange Instability in the Magnetotail
AU: * Pritchett, P L
EM: pritchet@physics.ucla.edu
AF: Department of Physics and Astronomy, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1547 United States
AU: Coroniti, F V
EM: coroniti@astro.ucla.edu
AF: Department of Physics and Astronomy, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1547 United States
AB: The classical ballooning mode is driven by a large enough pressure gradient in the same direction as the magnetic curvature. An alternative driver for interchange/ballooning modes in a high beta system is a tailward-directed gradient in the equatorial magnetic field profile such as is frequently formed in the magnetotail during extended periods of plasma-sheet convection. A massively parallel 3-D PIC code is used to determine the properties of this mode. The linear mode spectrum is dominated by relatively short wavelengths satisfying k_y ρ_in ~ 5, where ρ_in is the ion gyroradius in the local normal magnetic field. The observed growth rate is γ/Ω_i0 ~ 0.1, which is much smaller than predicted by a simple fluid analysis. A kinetic treatment is used to obtain this result. The real frequency is comparable to the growth rate, and the phase velocity is directed in the direction of the ion drift. Nonlinearly, the mode evolves to produce the classic extended fingers of the Rayleigh-Taylor instability. The mode does not lead to a disruption of the global current sheet, but it does produce a local dipolarization. Further implications for magnetotail dynamics will be discussed.
DE: 2744 Magnetotail
DE: 2764 Plasma sheet
DE: 2772 Plasma waves and instabilities
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly