PARTICLE-ACCELERATION DURING SUBSTORM GROWTH AND ONSET

We present ISEE‐1 observations of ion and electron energization made at ∼11 RE during a substorm event occurring on 2 April 1978. An analysis of the dominant cross‐tail current systems in this event (Mitchell et al., 1990) has allowed us to uniquely associate particle energization processes with the development and/or disruption of the cross‐tail currents. We find that significant ion acceleration occurs as the ions participate in serpentine cross‐tail motion (Speiser, 1965), establishing the dominant plasma sheet current system just prior to onset. As this current disrupts, the magnetic field configuration dipolarizes and further ion energization and the bulk of the electron energization occurs. During dipolarization energization is due primarily to the inductive electric field, including betatron and Fermi acceleration processes. Copyright 1990 by the American Geophysical Union.