Energetic particle bursts before the main substorm injection Original Research Article

We examine the relationship between the energetic electron bursts (15 – 30 s) observed before the main injection and the changes in the magnetic field during substorms on the CRRES. Pitch angle distrubution (PAD) of electron flux during these bursts and injections depends on the spacecraft position relative to the cross-tail current sheet and boundaries of energetic particle trapped region. Near the inner edge of plasma sheet (PS) the pancake PAD was observed. Inside the PS and near the outer energetic particle trapped boundary the cigar and isotropic PADs were observed. The lack of dispersion in some observed injection events are evidence of local acceleration. The burst onsets correlate with the magnetic bursts of ∂Bz/∂t with the time duration ∼ 2–4 s. It is likely that particles are accelerated by induced E field arising from these observed magnetic bursts.