HR: 10:45h
AN: SM22A-02    [Abstracts]
TI: Geotail Observations of the Spatial Dependence of Kelvin-Helmholtz Waves on an Inbound Passage Through the Dusk Flank Boundary Layer
AU: * Fairfield, D H
EM: Donald.H.Fairfield@nasa.gov
AF: NASA Goddard Space Flight Center, Code 695, Greenbelt, MD 20771 United States
AU: Farrugia, C J
AF: Space Science Center, University of New Hampshire, 39 College Rd, Durham, NH 03824 United States
AU: Gratton, F T
AF: Instituto de Fisica del Plasma,CONICET and FCEyN, University of Buenos Aires, Buenos Aires, Argentina
AU: Mukai, T
AF: Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510 Japan
AU: Nagai, T
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, 152-8551 Japan
AB: On August 1, 1998, the Geotail spacecraft made an inbound passage perpendicular to the dusk magnetopause at the dusk terminator when the interplanetary magnetic field had been very northward for more than 10 hours. Typical 3-minute-period Kelvin-Helmholtz waves were observed and the density in the boundary layer and magnetopause was observed to have an unusually high value near 5 /cc. Compressible MHD calculations using the measured values at Geotail yield substantial growth rates that support the idea that the magnetopause was Kelvin-Helmholtz unstable. In contrast to many previous events where a spacecraft remained in the boundary layer, this passage allowed study of how the waves varied with distance inward from the magnetopause. In a layer adjacent to the magnetosheath, rapid magnetic field fluctuations were seen with variations of at least 50 nT/s. As the spacecraft approached the magnetopause from the magnetosheath the boundary waves led to transitions between the magnetosheath and the fluctuating region with its magnetosheath-like densities and tailward velocities. As the spacecraft moved inward, the transitions were more likely to be between the fluctuating region and a hotter region with magnetosphere-like densities of 5/cc. Gradually the velocity perturbations began to exhibit 360 degree rotations. Such rotations are similar to the vortices seen earlier by the ISEE spacecraft throughout the magnetotail which were suspected of being caused by Kelvin-Helmholtz instability of the boundary.
DE: 2731 Magnetosphere--outer
DE: 2744 Magnetotail
DE: 2748 Magnetotail boundary layers
DE: 2752 MHD waves and instabilities
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly