UCLA

Ultra Low Frequency (ULF) waves are an important mechanism for energy transfer in the Earth's magnetosphere, interacting with a variety of different plasma populations and other plasma wave modes. The solar wind is an important energy source for ULF waves, and there are many pathways through which solar wind energy can drive wave activity. In this thesis, two case studies and two statistical studies are presented to demonstrate the manner in which energy is transferred from the solar wind to magnetospheric ULF waves. These studies demonstrate the viability of both the field line resonance paradigm and global fast (cavity/waveguide) modes as pathways for energy transfer from the solar wind to various sinks of wave energy in the magnetosphere. They also show that the plasmasphere plays an important role in suppressing electromagnetic energy transfer via ULF waves from the solar wind to the inner magnetosphere in the Pc5 frequency band.

The first case study demonstrates the conversion from isotropic to perpendicular energy flux at the field line resonance (FLR) location, providing further validation for the FLR paradigm. The second case study demonstrates that solar wind dynamic pressure fluctuations with a broadband frequency spectrum provide energy to drive a monochromatic global (cavity/waveguide) mode, which in turn provides energy to drive shear Alfv en waves through FLR; this is the first direct observation of energy transfer via a global mode in the Pc5 (2-7 mHz) frequency band outside of the plasmasphere. The first statistical study demonstrates that Pc5 electric and magnetic field perturbations have significantly lower amplitude in the plasmasphere compared to the low density region outside the plasmasphere; this suggests that ULF wave electromagnetic energy incident from the outer magnetosphere is not easily transferred across the plasmapause boundary in the Pc5 frequency range. The second statistical study characterizes global mode waves and provides a lower bound for the occurrence rate, or total time that global modes are observed divided by total observation time, of 1.0%.