Authors

L. R. Lyons1,C.-P. Wang1, T. Nagai2,T. Mukai3,Y. Saito3,J. C. Samson4

1  Department of Atmospheric Sciences
University of California, Los Angeles
Los Angeles, CA 90095-1565

2  Department of Earth and Planetary Sciences
Tokyo Institute of Technology
Ookayama 2-12-1, Meguro
Tokyo 152-8551, Japan

3  Institute of Space and Astronautical Science
3-1-1 Yoshinodai, Sagamihara
Kanagawa 229-8510, Japan

4  Department of Physics
University of Alberta
Edmonton, Alberta T6G 2J1

,J. Geophys. Res., 108 (A12), 1426, doi: 10.1029/2003JA010177, 2003

Abstract

Geotail measurements from within the equatorial inner plasma sheet at r ~10-13 RE are used to show that a reduction in equatorial plasma pressure within the current wedge is a general feature of substorms, and that this decrease is simultaneous with the well-known expansion phase increase in energetic particle fluxes. The decrease in pressure is found to be due to a decrease in particle fluxes at lower energies that gives a significant decrease in plasma density. We also find that, when viewed as a function of the adiabatic energy invariant for the plasma sheet ă, there is a reduction in the number of particles for all ă despite the enhancements seen when energetic particle fluxes are viewed at fixed particle energy. These observations demonstrate that the expansion phase is associated with a significant reduction in flux tube content of particles within the current wedge, and that this reduction leads to the expansion-phase reduction in equatorial plasma pressure and cross-tail current.

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