Energetic particles in the earth's magnetospheric cusps
Walsh, Brian M.
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The Earth's magnetic cusps are the regions with the most direct transfer of energy, mass, and momentum from the flowing solar wind to the Earth's magnetosphere. Spacecraft observations in the cusp have revealed a high energy component to the thermal particle distribution. This has raised the question as to whether significant plasma heating may also be occurring in this region. Since the cusp is magnetically connected to a number of other regions in geospace, plasma heating in this region could be a significant contributor to magnetospheric dynamics. The goal of this thesis is to answer the question, what is the source of the energetic particle population in the cusp? Since the initial observations measuring the energetic component were made, the source of the energetic population has been open to conjecture. A number of sources have been proposed: (1) the terrestrial bow shock, (2) the Earth's high-latitude trapping region, and (3) heating of plasma locally in the cusp. Depending on which source is the dominant provider of the energetic particles, the particle population will exhibit different properties. Particle flow direction, intensity, spectral characteristics, and species/charge state are all properties that can change depending on the dominant source. In-situ measurements by the ISEE, Polar, and Cluster spacecraft are used to derive the particle properties. These properties are compared with predictions for each of the proposed sources to determine which is most consistent with the observations. Case studies show that, under different conditions, the high-latitude trapping region and local heating can both be the dominant source of the energetic particle population up to energies of hundreds of keV. Results from a large scale statistical study, however, are more consistent with local heating indicating that this is the dominant source the majority of the time.
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