Cluster observations of geomagnetic storms and of magnetospheric substorm 
behavior in the near- and mid-tail regions

D.N. Baker, W. Peterson, R. Ergun, S. Eriksson, J. Blake, J. Burch, P. Daly, E.
Donovan, M. Dunlop, H. Frey, R. Friedel, T. Fritz, A. Korth, S. Mende, J. Roeder,
and H. Singer


The Cluster constellation of spacecraft have returned a wealth of new data on
particle and field variations in the near- and mid-magnetotail regions of Earth's
magnetosphere. Using the Research with Adaptive Particle Imaging Detectors
(RAPID) systems onboard the four Cluster vehicles, we have identified 
substorm-related energetic (E > 20 keV) electron enhancement events during the 
period March 2001 through October 2001 in the geocentric radial range of 4 to 19 
Earth radii. We have used concurrent data from other Cluster instruments as well 
as from the IMAGE, FAST, GPS, and geostationary orbit spacecraft in order to 
understand particle injection and transport phenomena throughout this key region 
of the magnetotail. One particularly striking event during a major geomagnetic 
storm on 31 March 2001 showed a dispersionless electron injection event in as 
close to the Earth as 4 Re. More normal electron enhancements in the plasma 
sheet at intermediate radial distances are also studied in a global substorm 
context. A particularly well-observed substorm case occurred on August 27, 2001 
when CLUSTER was almost exactly in the midnight meridian and complementary data 
were available from IMAGE, POLAR, GOES-8, and the LANL satellites. We find 
evidence that CLUSTER was very near the near-Earth substorm neutral line and 
that magnetic reconnection began some seven minutes prior to the substorm 
auroral brightening of the expansive phase onset.

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Presented at the 34th COSPAR Scientific Assembly, Houston, Texas, U.S.A.  
10-19 October 2002