Graduation Semester and Year
Summer 2025
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Physics and Applied Physics
Department
Physics
First Advisor
Yue Deng
Abstract
In this dissertation, the inter-hemispheric asymmetries (IHAs) in the ionosphere–thermosphere (I-T) system and their impacts on the coupled magnetosphere-ionosphere–thermosphere (M-I-T) were examined using multi-instrument observations and advanced global numerical modeling frameworks. First, the drivers and consequences of IHAs in the I-T were systematically investigated and quantified, revealing that seasonal solar irradiance differences, geomagnetic field offsets, and asymmetric high-latitude electrodynamic forcing each produce significant asymmetries in electron density, neutral density, velocity, and Joule heating, with seasonal effects dominating under relative quiet conditions. During geomagnetic storms, IHAs were found to depend more strongly on asymmetric field-aligned currents (FACs) and particle precipitation (PP), with FACs exerting a more spatially structured influence than PP, and IMF By polarity further modulating the response. Storm-time IHAs were shown to be scale- and driver-dependent, with spatial asymmetry patterns often more important than magnitude differences; to better represent these effects, a spatial asymmetry index was introduced to capture the spatial variations of IHAs. Second, the impacts of I-T IHAs such as ionospheric conductance and thermospheric neutral wind-driven currents on the magnetosphere through M-I coupling were explored with case studies of the December 2021 Antarctic total solar eclipse and the May 2024 superstorm. These studies demonstrated that eclipse-induced conductance reductions can significantly alter polar cap potentials and total FACs, reduce their IHAs, and drive dynamic changes in the magnetosphere, including modification in plasma flows and large-scale magnetospheric structure. In addition, neutral-wind–driven currents have been shown to play a more significant role in geomagnetic disturbances (GMDs) than commonly assumed—especially at mid-latitudes during storm recovery phases. This finding highlights the urgent need to more accurately represent wind-driven current effects in M–I–T coupling models. Finally, the importance of multi-satellite constellation to resolving multiscale neutral density variations was assessed using GRACE satellite observations and virtual satellites from GITM simulations. Results highlighted how different multi-satellite configurations can resolve temporal and spatial scales of neutral perturbations during storm times, providing new insights for future missions such as NASA’s Geospace Dynamics Constellation (GDC). The findings emphasized that both mesoscale and large-scale structures must be captured to fully characterize storm-time thermospheric variability. These results advances our understanding of the IHAs in the I-T system and how these IHAs shape the M-I-T system. Together, this dissertation enhances our understanding of geospace through a comprehensive approach that integrates theoretical interpretation, advanced numerical simulations, and innovative observational designs. These results provide a foundation for improving space weather prediction, highlight the value of integrating comprehensive physical mechanisms in space physics.
Keywords
Inter-hemispheric asymmetry, Magnetosphere-ionosphere-thermosphere coupling, Numerical simulation, High-latitude electrodynamics, Field-aligned currents, Particle precipitation, Magnetospheric convection, Neutral density, Ionospheric conductivity
Disciplines
Geophysics and Seismology
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Hong, Yu, "Inter-Hemispheric Asymmetry in the High-Latitude Electrodynamics and Their Impacts on the Magnetosphere-Ionosphere-Thermosphere System" (2025). Physics Dissertations. 183.
https://mavmatrix.uta.edu/physics_dissertations/183