- Title
- ULF modulation of EMIC in the inner magnetosphere
- Creator
- Williams, Joshua
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Electromagnetic Ion Cyclotron (EMIC) Waves are important in magnetospheric wave-particle interactions leading to depletion of radiation belt MeV electron populations and erosion of ring current keV ions. A subset of these, Pearl-EMIC waves, exhibit regular time varying amplitude for which the mechanism is unclear. Past ground and satellite observations of these waves with longer period ULF waves have implied this mechanism may be related to changes in the EMIC growth rate by Pc4/5 waves. Two pearl-EMIC wave events each from field data obtained from the RBSP-A and CRRES satellites (four in total) with wave packet periodicities similar to concurrent Pc4/5 ULF wave frequencies are examined using available in-situ plasma and field data. Events were inside density enhancements or close to the inside edge of the plasmapause. EMIC wave packets occurred preferentially (although inconsistently) in the troughs of the ULF wave compressional component and correlated with enhancements in the 10’s keV energetic protons and heavy ion pitch angle fluxes (where available) near 90 degrees, indicating anisotropy modulation. Linear temporal and convective growth rate analyses and hybrid-PIC simulations indicated these waves were grown from nearby generation regions. Growth rate modulation was observed, driven by both changes in the total magnetic field and proton anisotropy. Simulation results showed that a decrease in field magnitude alone may be sufficient to grow marginally stable populations to an observable level, although this is equivalent to starting with a more unstable population. Comparison with nonlinear threshold amplitudes for two events also show that pearl-pulsations may be grown linearly by modulated ion parameters, then transition into a rising tone structure. This was confirmed by a hybrid simulation with a non-uniform background magnetic field, and may be related to EMIC triggered emissions. These results add to the scant catalogue in the literature of ULF wave modulated pearl-EMIC emissions and provide in situ evidence of the growth rate modulation based on spacecraft data. Further work is required to model the observed EMIC-ULF relationships in a driven dynamic hybrid model.
- Subject
- EMIC waves; magnetospheric physics; wave particle interactions; ULF waves; hybrid simulation; numerical simulation; pearl pulsations; ULF modulation; Pc1
- Identifier
- http://hdl.handle.net/1959.13/1468055
- Identifier
- uon:47981
- Rights
- Copyright 2022 Joshua Williams
- 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 | 96 KB | Adobe Acrobat PDF | View Details Download |