UCLA

This dissertation presents a systematic study of the equatorial magnetosonic waves in the Earth's inner magnetosphere, addressing important issues which include the global distribution, energy source, propagation properties, and potential scattering effects. Equatorial magnetosonic waves are highly oblique whistler-mode electromagnetic emissions between the proton gyrofrequency and the lower hybrid resonant frequency, widely distributed in the Earth's inner magnetosphere, and may potentially cause electron acceleration in the radiation belts. The recent equatorial spacecraft THEMIS and the Van Allen Probes provide excellent observations on equatorial plasma waves. A global survey of magnetosonic waves is performed using THEMIS wave data products. The statistics show that the most intense magnetosonic waves are distributed near the dayside outside the plasmapause, with maximum root-mean-square averaged wave amplitudes between 50 and 100 pT and occurrence rates between 10% and 40%. An instability analysis is performed on a typical magnetosonic wave and locally observed ion ring distribution event. The unstable ion ring distribution could provide free energy for the wave excitation outside the plasmapause or in the outer region of the plasmasphere. Although magnetosonic waves cannot be excited deep inside the plasmapause, the waves observed there can originate from the outer region and remain trapped in the plasmasphere. The wave perpendicular propagation analysis demonstrates the importance of wave trapping in explaining the wave existence in the plaspasphere. The magnetosonic waves can cause electron pitch angle and energy scattering via Landau resonance and transit time effects, which lead to electron acceleration in the radiation belts. The investigation of their influences on energetic electrons in the Earth's inner magnetosphere shows that the acceleration time scale is generally tens of days. Using both observational and modeling techniques, this thesis provides comprehensive information about equatorial magnetosonic waves in the inner magnetosphere.