Three‐satellite measurements and field‐line mapping of the outer plasma sheet boundary from r ∼1.2 to ∼18 RE during substorms

Simultaneous and near-conjugate observations of energetic particles in the outer region of the plasma sheet by three satellites (Esro 1A, Ogo 5, and Vela 5B) shoe clear indications of a close relationship between the instantaneous latitudinal location of the high-latitude precipitation boundary at 1000 to 1500 km height and the thickness of the plasma sheet at geocentric distances of 10 to 18 R/sub E/. By comparing low-altitude and magnetotail particle energy spectra and by using recent magnetospheric field-line models as spatial reference systems, we find evidence that the precipitation boundary and the outer plasma sheet boundary are magnetically connected. The correlation between plasma sheet recovery and a poleward expansion of the precipitation boundary from Aapprox.70/sup 0/ to approx.75/sup 0/ late in substorms suggests that this recovery is associated with rapid magnetic field-line reconnection as the reconnection region apparently moves to a more distant location in the tail.