Author ORCID Identifier

https://orcid.org/0000-0002-6113-3945

Semester

Summer

Date of Graduation

2025

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Weichao Tu

Committee Co-Chair

Paul Cassak

Committee Member

Christopher Fowler

Committee Member

Lauren Blum

Abstract

Energetic electrons in the terrestrial outer radiation belt present significant hazards to spacecraft systems and human operations in space. The intensity of these electrons can vary rapidly and dramatically during geomagnetic storms, governed by a complex competition between acceleration and loss processes. Among these, precipitation into the atmosphere via resonant wave-particle interaction acts as a key loss mechanism. This dissertation focuses on improving the quantification of energetic electron precipitation using physics-based modeling constrained by low-altitude satellite observations.

We begin by developing and validating the Drift-Diffusion model, which simulates low-altitude electron dynamics while accounting for azimuthal drift, pitch-angle diffusion, and atmospheric backscatter. Using data from the POES/MetOp satellite constellation, we constrain the model to infer event-specific diffusion rates based solely on observed low-altitude electron distributions. Applying this method to an event on August 21, 2013, we show that precipitation dominates the loss near L=4.5 (approximately equal to radial distance in units of Earth radii) for electrons below ~850 keV. This approach enables the separation of precipitation from other loss or acceleration mechanisms without relying on sparse high-altitude satellite wave measurements.

Building on this, we apply a novel version of the Drift-Diffusion model to reconstruct the spatiotemporal evolution of plasmaspheric hiss wave power responsible for a precipitation event on October 15, 2016. By redefining the model parameters in terms of wave properties, we use low-altitude observations to infer the spatial distribution and evolution of wave power. The quantified wave power agrees well with in-situ observations from Van Allen Probes, and the spatial evolution is consistent with previous statistical and machine learning studies. Furthermore, the model suggests the presence of undetected “low”-frequency plasmaspheric hiss, likely masked by instrument noise. This approach of using low-altitude data to constrain event-specific wave power distribution is critically important in accurately quantifying energetic electron precipitation, and its atmospheric consequences.

Finally, we address a key limitation in bounce-averaged pitch-angle diffusion models: their inability to accurately represent loss cone fluxes due to the neglect of atmospheric backscatter. Using Geant4-based simulations, we estimate and quantify the effects backscatter as two separate processes, backscatter-induced pitch-angle diffusion (Db), and attenuation of atmospheric absorption (Fb). Incorporating these effects into a modified pitch-angle diffusion model, we compare ELFIN satellite observations during Electromagnetic Ion Cyclotron (EMIC) wave-driven precipitation events, and demonstrate that by including backscatter, it resolves the previously unexplained enhancements in the loss cone flux for electrons below ~300 keV.

Together, these studies advance the modeling of energetic electron precipitation in the outer radiation belt, reduce reliance on limited in-situ wave measurements, and ultimately improve the ability to assess precipitation loss into the atmosphere and to understand its atmospheric consequences.

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