Survey of dispersionless substorm ion injections observed by CRRES

We present an analysis of the composition and nature of 87 dispersionless energetic (40-400 keV) ion injections observed by the MICS ion spectrometer instrument onboard CRRES during the first half of 1991. During this period the CRRES geostationary transfer orbit provided good coverage for all local times from 18:00 to 02:00, with magnetic latitudes and L-Shells in the ranges ± 30 degrees and 4 to 8 R _E respectively. Dispersionless ion injections are associated with substorm expansion phase onset. Each injection event has been classified in terms of composition (solar wind or ionospheric rich) and prevailing magnetospheric conditions (represented by Dst). The resulting database (after correction for spacecraft sampling effects) has been used to investigate the observed spatial distribution of the events as a function of composition and Dst. These preliminary investigations illustrate the large spatial extent of dispersionless ion injections (with O ⁺ dominating at earlier MLT) and the sharp (Dst independent) cut off of the MLT distributions at local midnight. We suggest that this corresponds to the 'average' eastern extent of the ion injection region. Furthermore, we suggest that substorms can inject particles into the ring current.