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The Effectiveness of EMIC Wave-Driven Relativistic Electron Pitch Angle Scattering in Outer Radiation Belt Depletion


The dynamic variability of Earth's outer radiation belt is due to the competition among various particle transport, acceleration, and loss processes. The following dissertation investigates electron resonance with Electromagnetic Ion Cyclotron (EMIC) waves as a potentially dominant mechanism driving relativistic electron loss from the radiation belts. EMIC waves have been previously studied as contributors to relativistic electron flux depletion. However, assumed limitations on the pitch angle and energy ranges within which scattering takes place leave uncertainties regarding the capability of the mechanism to explain sudden loss of core electron populations of the outer radiation belt. By introducing new methods to analyze EMIC wave-driven scattering signatures and relativistic electron precipitation events through a multi-point observation approach, this dissertation reveals the effectiveness of EMIC waves to drive losses of outer radiation belt electrons with a new resolution.

The research that composes this dissertation focuses on three key areas of the EMIC wave-relativistic electron relationship. A chapter comparing a single EMIC wave event with a pitch angle scattering signature shows that these waves can cause scattering of electrons at energies and pitch angles predicted by the wave-particle resonance condition. This initial study establishes the motivation and methodological groundwork for a statistical study which provides evidence for the common occurrence of these scattering signatures and shows that the energies and pitch angles affected by EMIC waves are often within the core radiation belt population.

A subsequent study then links scattering signatures to observations of relativistic electron precipitation events, revealing a significant coincidence rate between EMIC waves and precipitation events.

These three investigations together provide the first quantifiable tracing of relativistic electron precipitation events back to the driving EMIC wave, through verified scattering signatures. The results support EMIC wave-relativistic electron resonant interaction theory and provide strong quantitative evidence that EMIC waves can effectively drive losses of core radiation belt electrons.

The new knowledge gained here benefits the space physics community by informing space weather modelers and forecasters of the conditions that increase the efficiency of EMIC wave-driven radiation belt losses, and by introducing new and effective ways of identifying and analyzing EMIC wave-driven scattering to be used in future investigations.

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