Authors

C.-P. Wang1, L. R. Lyons1, T. Nagai2,J. C. Samson3

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

J. Geophys. Res., 109, A12201, doi:10.1029/2004JA010590, 2004

Abstract

To evaluate the plasma sheet transition from weak to strong convection, we investigate ion moments and magnetic field observed by Geotail. The Geotail data from 1995 to 1997 within the area 9 RE XGSM 30 RE and jYGSMj 5 RE were sorted for periods of quiet times and the substorm growth phase, which gives a better indication of convection strength than do global indexes. We find that the overall growth-phase ion pressure is a factor of 1.55 higher than the quiet-time ion pressure. Density is higher and temperature is lower during quiet times. Ions drift mainly earthward and duskward, and the drift speed is about twice stronger during the growth phase. The duskward drift is dominated by ionsŐ diamagnetic drift. The jBxj in the lobes increases strongly, while Bz near the current sheet at small radial distance decreases as convection increases, indicating that field lines become more stretched during the growth phase because of the earthward penetration of the plasma sheet. The increase in the lobe magnetic field is sufficient to maintain force balance in the z direction with the enhanced ion pressure in the plasma sheet. Intervals of negative Bz are observed during both quiet and growth-phase conditions. The observed negative Bz intervals near the current sheet are short and are likely caused by perturbations, while those in the lobes are substantially longer and are likely associated with field line flaring.

All full manuscripts and figures are available in PDF format only. For another format or hardcopies you will need to contact the Authors.

Paper and Figures (pdf format)