Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
The Ionosphere-Thermosphere (I-T) system is greatly affected by the magnetospheric energy deposition from above and subjected to forcing from the lower atmosphere simultaneously. A central problem in studying the coupled I-T system is to analyze the multi-scale processes naturally embedded in both ways. Magnetospheric energy input such as auroral precipitation and electric field demonstrates multi-scale structures during magnetic storms, resulting in multi-scale I-T responses when deposited into the I-T system. To better quantify the multi-scale aurora and electric field, we developed a new data assimilation model based on a multi-resolution Gaussian process model to synthesize empirical models and observational data from various sources and provide estimates in regions without observations. The new method mitigates the discrepancy between empirical models and observations by successfully capturing the dynamic evolutions of large-scale and mesoscale auroral and electric field structures. By further incorporating the assimilated aurora and electric fields into Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) during the 2015 St. Patrick's Day storm, we significantly elevate Joule heating and largely reproduce the global and local I-T responses as observed, including the enhanced electron density and vertical wind. Data assimilation also helps introduce more spatial and temporal variabilities in TIEGCM, which propagate to low-latitude regions through Traveling Atmospheric Disturbance (TAD). In the other direction, to study the atmospheric wave forcing from below and how it impacts the I-T system, we develop a nested-grid extension to TIEGCM to study the Gravity Wave (GW) propagation process and its ionospheric effect during the 2022 Tonga volcano eruption. Such a hybrid-grid design helps to better simulate the variations of a smaller scale than the standard model resolution while reducing computation costs at the same time. With proper seeding at the lower boundary, GW propagation in the thermosphere is successfully reproduced. The resulting Traveling Ionospheric Disturbance (TID) in the ionosphere has a similar speed to observations. The wave spectrum at different altitudes also indicates that the dominant GW has a shorter period and horizontal wavelength at higher altitudes. This dissertation discusses the detailed tool development, including data assimilation and TIEGCM-NG, which enables a better understanding of the influences of multi-scale magnetospheric forcing and lower-atmosphere wave forcing on the I-T system. This work provides a powerful set of tools for a better simulation of space weather.
Wu, Haonan, "Studies of the Ionosphere-Thermosphere Responses to Multi-Scale Energy Deposition Processes" (2023). All Dissertations. 3276.
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