UCLA

Resonant interactions between energetic radiation belt electrons and equatorially-generated whistler-mode waves are widely studied because they yield either electron acceleration or precipitation -- where electrons are scattered and lost into the Earth's atmosphere -- both of which are fundamental to space weather forecasting, which is an increasingly relevant challenge as society scales up its reliance on space technologies. This dissertation investigates the mechanisms that govern the effectiveness of electron losses from Earth's radiation belts driven by whistler-mode waves using novel electron precipitation measurements from the ELFIN CubeSats. A culmination of innovative engineering efforts and a refactored satellite operations program has allowed ELFIN to obtain over 12,500 high-quality, low-altitude electron measurements of the radiation belts. These measurements are uniquely capable of resolving the bounce loss cone, allowing us to probe the physics that drive electron precipitation in great detail. We first present a test particle simulation that directly compares ELFIN-measured electron precipitation with equatorial electron and wave measurements by the THEMIS and MMS spacecraft during magnetic conjunctions, confirming the importance of mid-high latitude wave-power. Next, we demonstrate that test particle simulations combined with an empirical wave amplitude model adequately approximate statistical ELFIN observations at the dawn, day, and dusk MLT sectors, but they significantly underestimate relativistic (>500$keV) electron losses on the nightside. To resolve this discrepancy, we additionally use quasi-linear diffusion simulation methods to find that considering wave obliquity, wave frequency, and plasma density together are required to recover the energetic portion (>100 keV) of precipitating electron spectra without overestimating the loss contributions from the quasi-linear regime (~100 keV). We conclude by presenting the ranges of wave and plasma characteristics necessary for the incorporation of accurately modeled electron loss rates into modern radiation belt models. This unlocks the potential to remotely sense equatorial wave properties using electron precipitation measurements, but also calls for future \textit{in situ} satellite experiments to more deeply understand the interconnected role of energetic electron losses in atmospheric, ionospheric, and magnetospheric dynamics.