posted on 2015-07-08, 13:50authored byMatthew 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.