A multisatellite study of the plasma sheet dynamics at substorm onset

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Abstract
A multi‐satellite study has been conducted on the temporal relationship between energetic particle injections observed at the geostationary orbit onboard GEOS‐2 and decreases of thermal plasma sheet particle fluxes ("plasma sheet thinnings") observed in the more distant geomagnetic tail onboard the ISEE‐1 and ‐2 spacecraft. A case by case analysis as well as a statistical study of 100 events recorded from February to May 1979 and 1980 show that particle injection and particle flux decrease are detected to within less than 5 minutes of each other, for an average intersatellite distance of 15.7 RE. The observed spread in Δt corresponds best to Alfvén wave transit times. These particle phenomena are observed at the onset of the auroral zone magnetic bays. The results reported here suggest that the dynamics of the inner and outer boundaries of the plasma sheet are closely related to each other and controlled by large scale processes that develop at substorm onset inside the magnetospheric tail and result in a cross‐tail current disruption.