- Title
- The interaction of storm-time ULF waves with Earth’s radiation belts in the presence of a realistic ionosphere boundary
- Creator
- Shah, Asif
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The outer Van Allen radiation belt becomes unstable during geomagnetic storms, when the fluxes and energies of geomagnetically trapped particles fluctuate by several orders of magnitude. Ultra-low frequency (ULF) plasma waves are widely believed to play an important role in accelerating radiation belt particles to ‘killer’ energies that may damage space assets and contribute to other space weather hazards. Previous work on the role of these wave-particle interactions has usually focused either on in-situ observations or simulation studies. Most of the previous simulation studies have ignored the ionosphere boundary, or treated it as a perfectly conducting boundary in the ideal limit or as an electrostatic layer by ignoring the Hall conductivity. Although the polar ionosphere boundaries were included in the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model, the effect of ionospheric Pedersen and Hall conductances on wave-particle interactions was not studied. This thesis for the first time includes the effects of realistic ionosphere boundaries into test-particle simulations of ULF wave-particle interactions in Earth’s magnetosphere. The ionosphere boundary is characterized by finite and nonzero values of the height integrated direct, Hall, and Pedersen conductances. Four distinct studies are included in the thesis, each forming a manuscript to be submitted for publication or published in the peer reviewed literature. The first study shows that four types of ionosphere boundaries (ideal reflector, daytime with no Hall conductivity, realistic night-time, and realistic daytime) each result in unique distributions of kinetic energy and radial diffusion coefficients for equatorially mirroring electrons. It is also shown that the electron trajectory and kinetic energy for a perfectly conducting ionosphere temporally evolve in distinctly different ways from the temporal behaviours of electron trajectories and kinetic energies due to ULF waves modelled in the presence of realistic ionosphere boundaries. This study for the first time shows that treatments of ULF wave-particle interactions in the magnetosphere cannot ignore the effects of realistic ionosphere boundary conditions. The second study examines storm time in-situ observations of ULF waves and electron fluxes on 7 January 2011. A magnetohydrodynamic (MHD) model incorporating realistic ionosphere boundaries is used to simulate ULF wave propagation in the magnetosphere at this time. In these simulations the wave toroidal and poloidal electric fields are comparable to those measured by the THEMIS satellites during the event. Test-particle simulations of wave-electron interactions in the equatorial plane show flux enhancements which agree with observations from the THEMIS-A satellite. It is also shown that the temporal rate of electron energization increases with decreasing ionosphere conductance. The significance of the ionosphere conductance, the ULF wave frequency, and particle trapping due to field line resonances (FLRs) are examined. The third study examines storm time in-situ observations of ULF waves and proton flux enhancements on 8 October 2013. The MHD model of ULF wave propagation is used with realistic dusk side values of the Hall and Pedersen conductances. The simulations produce wave electric fields comparable with those measured by the electric field and wave (EFW) instruments on the Radiation Belt Storm Probes (RBSP) satellites, and the electric field instrument (EFI) on the THEMIS-E satellite. Test-particle simulations are used to examine the evolution of wave-particle interactions at various locations off the equator. Proton flux observations are explained via these simulations. It is also shown that increasing ionospheric Hall and Pedersen conductances decrease the amplitudes of the wave electric fields, which in turn reduces proton energization. The fourth study shows that when the north and south ionosphere boundaries are symmetric then the amplitudes of the toroidal and poloidal electric fields in the northern and southern hemispheres are also equal. However, for asymmetric ionosphere boundaries high amplitude ULF electric fields occur in the hemisphere with small values of ionosphere conductances. The effects of symmetric and asymmetric ionospheres are compared with the energization of bouncing and drifting protons via test-particle simulations of ULF wave-proton interactions.
- Subject
- magnetospheric particle energization; ULF waves; ionosphere boundary; geomagnetic storms; Van-Allen radiation belts
- Identifier
- http://hdl.handle.net/1959.13/1354289
- Identifier
- uon:31247
- Rights
- Copyright 2017 Asif Shah
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 6 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 586 KB | Adobe Acrobat PDF | View Details Download |