ULF waves driven by recently-injected energetic particle populations
thesisposted on 08.07.2015, 13:50 by Matthew Knight James
This thesis studies the characteristics of ultra low frequency (ULF) waves driven by recently-injected energetic particle populations gradient-curvature drifting azimuthally around the Earth. A statistical study of 83 separate substorm-driven ULF waves is undertaken in order to determine if the spatial proximity to the driving substorm affects the characteristics of the observed waves, as suggested by Yeoman et al. (2010). Waves were observed using Super Dual Auroral Radar Network (SuperDARN) radars and substorms identified using the Far Ultraviolet Imager (FUV) on-board the IMAGE spacecraft alongside a list of substorms provided by Frey et al. (2004). Azimuthal wave numbers, m, ranged in magnitude from 2 - 60 corresponding to particle energies, W, of ~1 - 70 keV. Phase propagation was always directed away from the location of the substorm and predicted particle energies were highest when closest to the substorm location in azimuth. This thesis also includes the study of three individual substorms, each with associated observations of multiple ULF waves using different SuperDARN radars. It is demonstrated that individual substorms are capable of driving a number of wave events characterised by different azimuthal scale lengths and wave periods, associated with different energies in the driving particle population. Similar trends in m and W are found to exist for multiple wave events with a single substorm as was seen in the single wave events of the statistical study. A recent case study event is included where substorm triggered ULF wave activity observed by two SuperDARN radars and observations of the particle populations responsible for driving the waves were observed using in-situ magnetospheric data from the Van Allen Probes. This conjunction of the recently-injected cloud of energetic ions with the probes allowed the study of the ion distribution functions which could then be compared to particle energies estimated using the characteristics of the waves.