HR: 14:10h
AN: SM32C-03    [PDF]
TI: Static Pressure Distribution in the Distant Tail Lobe and Compressional Variations Observed by Geotail
AU: * Matsuoka, A
EM: matsuoka@stp.isas.ac.jp
AF: Institute of Space and Astronautical Science, Yoshinodai, Sagamihara, Kanagawa, 229-8510 Japan
AB: In order to study the dynamics of the magnetosphere, it is important to know the temporal variation and spatial distribution of the static pressure. The static pressure in the magnetotail basically depends on the distance from the earth and also on the solar wind condition. We have statistically analyzed the static pressure measured by GEOTAIL in the magnetotail (X $<$ -40 RE) and extracted an empirical equation to express the static pressure in the tail lobe by the solar wind parameters. In the calm magnetosphere, the total pressure in the tail lobe is often smaller than the static pressure in the solar wind ($<$74%). For more than 90 % of the 30-minutes averaged data, the deviation of the measured pressure from the expected one is found to be within 50 %. On the other hand, substantial deviations of the measured static pressure from the expected one are often caused by the passage of plasmoids. An example of the static pressure variation in the distant magnetotail lobe caused by the passage of a plasmoid is investigated in detail. The traveling speed of the plasmoid is estimated to have been faster than the concurrent magnetosonic speed in the lobe. The magnetic field variation along the maximum variance direction was linearly related to the variation in the field strength, which suggests that a magneto-hydrodynamic compressional mode might have occurred. The propagation direction of the variation is determined from the background field direction and the maximum variance direction of the field. Shortly after the passage of the plasmoid, the relation between the field and velocity variations is consistent with the fast mode. Pressure variation in the fast mode was possibly generated in the trail of the plasmoid to restore equilibrium.
DE: 2731 Magnetosphere--outer
DE: 2740 Magnetospheric configuration and dynamics
DE: 2744 Magnetotail
DE: 2752 MHD waves and instabilities
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting