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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. A4, 1151, doi:10.1029/2002JA009544, 2003

Delivery of cold, dense plasma sheet material into the near-Earth region

M. F. Thomsen

Space and Atmospheric Sciences, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


J. E. Borovsky

Space and Atmospheric Sciences, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


R. M. Skoug

Space and Atmospheric Sciences, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


C. W. Smith

University of Delaware, Bartol Research Institute, Newark, Delaware, USA


Abstract

Observations from several satellites in geosynchronous orbit, combined with solar wind observations from the ACE spacecraft, demonstrate that cold, dense plasma sheet material can be delivered into the inner magnetosphere under two scenarios: (1) a sudden southward IMF preceded by an extended interval of northward field and (2) a very strong magnetospheric compression caused by a large increase in the solar wind dynamic pressure, also under conditions of northward IMF. Examination of 30 “superdense” plasma sheet events observed during 15 months in 2001 and 2002 shows that these two mechanisms are probably responsible for the occurrence of most superdense events, if “northward IMF” is generalized to “northward or very weak IMF Bz.” Previous work has shown that a superdense plasma sheet contributes to a strong ring current and geomagnetic disturbance if it is accompanied by strong magnetospheric convection (which requires southward IMF). Hence this study suggests that the formation of a strong geomagnetic storm should be favored by an extended interval of strong southward IMF that is preceded by an earlier interval of northward field or very weak Bz, during which the plasma sheet fills with cool, dense plasma.

Published 11 April 2003.

Index Terms: 2764 Magnetospheric Physics: Plasma sheet; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2760 Magnetospheric Physics: Plasma convection.

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Citation: Thomsen, M. F., J. E. Borovsky, R. M. Skoug, and C. W. Smith (2003), Delivery of cold, dense plasma sheet material into the near-Earth region, J. Geophys. Res., 108(A4), 1151, doi:10.1029/2002JA009544.