HR: 09:00h
AN: SM11B-05 INVITED    [Abstracts]
TI: Connections Between Plasma Sheet Transport, Region 2 Currents, and Entropy Changes During Substorms and SMCs
AU: * Lyons, L R
EM: larry@atmos.ucla.edu
AF: 1Department of Atmospheric and Oceanic Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095-1565, United States
AU: Wang, C
EM: cat@atmos.ucla.edu
AF: 1Department of Atmospheric and Oceanic Sciences, UCLA, 405 Hilgard Ave., Los Angeles, CA 90095-1565, United States
AU: Nagai, T
EM: nagai@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology I2-5, Ookayama 2-12-1 Meguro, Tokyo, 152-8551, Japan
AB: Modeling shows that energy-dependent magnetic drift leads to a divergence of particles and particle energy flux that gives significant violation of entropy conservation along the direction of the plasma bulk velocity. This is of critical importance to understanding the formation of the substorm growth-phase plasma sheet and the maintenance of a stable plasma sheet during SMC periods of prolonged enhanced convection. The particle divergence also is a divergence of the cross tail current, leading to the field-aligned currents that form the Region 2 system. Thus the Region 2 current system provides direct evidence that the modeled variations in entropy are reasonable. Shielding of the convection electric field from the inner magnetosphere is an aspect of the Region 2 system, so that the well-known development of shielding after a convection enhancement can be viewed as an additional signature of violation of entropy conservation. Region 2 field-aligned currents dramatically enhance during the substorm expansion phase in the vicinity of the Harang electric field reversal, signaling a region of greatly enhanced plasma sheet particle and current divergence. This enhanced divergence should also be a region of greatly enhanced divergence of particle energy flux, which should lead to significant reduction of plasma sheet entropy and pressure within the substorm current wedge, and such a reduction has been observed with Geotail. The observations also show a reduction of the flux tube content of particles over a broad range of invariant energies, despite the apparent injections of energetic particles inferred from fluxes measured at fixed particle energies. Evidence suggests that a reduction in the strength of earthward convection can initiate the enhanced divergence within the current wedge. Observations from the new ground radars and THEMIS will provide critical information for the evaluation and further understanding of the above processes.
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2744 Magnetotail
DE: 2760 Plasma convection (2463)
DE: 2764 Plasma sheet
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting