HR: 08:00h
AN: SM11B-01 INVITED    [Abstracts]
TI: Entropy and Plasma Sheet Transport
AU: * Wolf, R
EM: rawolf@rice.edu
AF: Physics and Astronomy Dept., Rice University, MS 108, P. O. Box 1892, Houston, TX 77251- 1892, United States
AB: Different entropy-related parameters are compared, along with the assumptions involved in their approximate conservation in Earth's plasma sheet. Our discussion centers on the entropy parameter PV^5/3, where V=volume per unit magnetic flux. It affects the structure and dynamics of the plasma sheet in several ways: (1) Earthward convection along with conservation of the entropy parameter leads to extreme stretching of inner- plasma-sheet flux tubes ("pressure crisis"). (2) Regions with an earthward gradient in the entropy parameter tend to be unstable to interchange, although there is still controversy about the exact instability criterion. (3) A localized region of reduced entropy parameter (bubble) moves earthward, causing a flow burst, in some instances; bubbles also apparently play a key role in ring current injection. The chief obstacle to understanding the role of entropy in plasma-sheet dynamics lies in the difficulty of measuring the flux tube volume V. We describe a method for estimating local V and entropy parameter from single-spacecraft measurements. It is not possible to test the algorithm against observations, but tests against a variety of models indicate that the mean error in the estimated V is about 8 per cent. The algorithm is based partly on the assumption of equilibrium and substantially underestimates the terminal value of the entropy parameter on flux tubes that are moving rapidly earthward.
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2752 MHD waves and instabilities (2149, 6050, 7836)
DE: 2764 Plasma sheet
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting