Composition and morphology of substorm-associated ion injections

• Main Author: Hall, Adrian Mark
• Published: University of Leicester 1997
• Subjects: 538
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696349

This thesis describes an investigation into the composition and morphology of substorm ion injections at magnetic latitudes and L-shells away from geostationary orbit. Furthermore, the work investigates the Dst-dependent conditions that affect these compositional and spatial characteristics. Count rate and composition measurements in the energy range 80 - 400 keV/q form the basis of the analysis. Near-equatorial observations by the CRRES spacecraft during 1991 have been used to study substorm and near-Earth magnetosphere composition, injection event distribution, and the injection region morphology. Measurements made by the Polar satellite during 1996 extend the study to high magnetic latitudes (50 - 60 °) and high L-shells (7 ≤ L ≤ 22), and are used to investigate the radial morphology of the injection region. For the first time, substorm injection rate as a function of composition, Dst, and injection type has been quantified. In storm time the rate more than doubles. This appears to result from the observed increase in the azimuthal extent of the average injection region. Analysis has shown however, that substorm onset and type (single or multiple injection events) are (for the most part) not significantly composition dependent. The threefold increase in ionospheric-rich event frequency during storm time is principally a result of the increase seen in the equatorial, dusk flank event occurrence. Ion injections have been observed over a large radial extent. Furthermore, ions drift coherently over a large range of L-shells, spanning, at times, from geostationary orbit to L ≈ 18. The inward transport of these ions is not composition dependent. The injected plasma depends on the magnetospheric composition tailward of the spacecraft. This is highly spatially variable and dependent on the past, and prevailing Dst conditions with large (fourfold) enhancements in ionospheric origin material observed inside of L ≈ 7 ( i.e. below the altitude of most substorm onsets) during storm time. The storm time nightside ring current is observed to expand both earthward and tail ward. Out of the equatorial plane, the injection rate is hypothesised to artificially decrease as a result of the tapered, crescent shaped form of the injection region.