HR: 11:50h
AN: SM22A-07    [Abstracts]
TI: Equatorial Distributions of the Plasma Sheet Ions, Their Magnetic and Electric Drifts, and Magnetic Fields Under Different IMF Bz Conditions
AU: * Wang, C
EM: cat@atmos.ucla.edu
AF: Dept. of Atmospheric and Oceanic Science, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095 United States
AU: Lyons, L
EM: larry@atmos.ucla.edu
AF: Dept. of Atmospheric and Oceanic Science, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095 United States
AU: Weygand, J
EM: jweygand@igpp.ucla.edu
AF: Dept. of Earth and Space Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095 United States
AU: Nagai, T
EM: nagai@geo.titech.ac.jp
AF: Tokyo Inst Tech Dept Earth & Planetary Sci, Ookayama 2-12-1 Meguro, Tokyo, 152-8551 Japan
AU: McEntire, R
EM: Dick.McEntire@jhuapl.edu
AF: Johns Hopkins Univ APL Space Physics Group, 11100 John Hopkins Rd, Laurel, MD 20723 United States
AB: To understand the nightside plasma sheet structure (X > -30 R_E) under different IMF Bz conditions, we have investigated statistically the equatorial distributions of ions and magnetic fields from Geotail when the IMF has been continuously northward or southward for duration shorter or longer than 1 hr. A dawn-dusk density (temperature) asymmetry with higher density (temperature) on the dawn (dusk) side is seen in the near-Earth plasma sheet during northward IMF, resulting in roughly dawn-dusk symmetric pressure. As southward IMF proceeds, the density asymmetry weakens while the temperature asymmetry maintains, resulting in higher pressure on the dusk side. The plasma sheet is relatively colder and denser near the flanks than around midnight regardless of the IMF conditions. The flux distributions show that the higher density regions on the dawn side and near the flanks are mainly due to ions < ~3 keV and that the temperature asymmetry is a result of the flux in the pre-midnight sector becoming increasingly higher with increasing ion energy. The perpendicular flow shows that ions divert around the Earth mainly through the dusk side in the inner plasma sheet due to westward diamagnetic drift. The flow pattern does not change significantly but the flow is stronger during southward IMF. The magnetic fields indicate that field-lines are more stretched during southward IMF. We are able to infer the electric potential from the observations and evaluate the ion's electric and magnetic drift paths. For thermal energy ions in the plasma sheet, magnetic drift is as important as electric drift. The distributions of the observed phase space density at different energies can be approximately accounted for by conserving the phase space density from the tail and flanks along the drift paths, indicating that transport by electric and magnetic drift and the associated adiabatic energization are responsible for the observed plasma sheet structures.
DE: 2463 Plasma convection (2760)
DE: 2744 Magnetotail
DE: 2764 Plasma sheet
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005