Global evolution of substorm electron injections

The evolution of the high-energy (>30keV) electron population during magnetospheric sustorms is understood almost exclusively in terms of particle measurements near geostationary orbit. Consequently, models of substorm associated enhancements in energetic electron flux (injections) are based on very little (if any) observational evidence outside of this region. This dissertation describes a new technique for identifying dispersionless electron injections using ground-based tools and several studies that are only possible with the resulting increase in observational capabilities.;Using data from an array of ground-based single beam riometers and the CRRES Medium Energy B (MEB) particle detector I show that it is possible to identify dispersionless injections without the energy resolved satellite measurements typically required to observe an injection. If the in situ total electron flux >30keV exhibits a dramatic rise within 3 minutes then the signature is guaranteed to correspond to a dispersionless injection. Since the Kennel-Petschek limit for strong pitch angle scattering is inherently met during substorm injections, this translates to an equivalent criterion for ground-based riometer absorption. I present statistical results for the onset location and evolution of the injection region as seen in the ionosphere. While ionospheric measurements do not directly contradict any in situ results, the models that have been put forward to describe the injection are not consistent with the ionospheric radial evolution of the injection region. To resolve this discrepancy I compare the delay between injection onset times observed at geosynchronous orbit and a second spacecraft in the same meridian but at a different radial distance. My results indicate that dispersionless injection is most likely to occur at magnetospheric radial distances of 6.7--9Re. The injection starts at this location and expands radially inward towards geosynchronous orbit, and outwards into the mid-tail central plasma sheet. I also find that the onset of injection, dipolarization and earthward flow in a given meridian are simultaneous. In a single case study of injection region evolution, the injection onset observed in riometer data (and confirmed by in situ measurements) occurs near geosynchronous orbit. These combined results led to a more complete phenomenological picture of injection region onset and evolution.