Experimental and Modeling Studies of the Morphology of Equatorial Ionospheric F-region Drifts
Shidler, Samuel A
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The Earth’s ionosphere is an ionized region of space in the upper atmosphere, starting around 80 km and extending to higher altitudes, comprised of ions and electrons made primarily from solar photo-ionization of neutral particles. Historically, the Earth’s ionosphere is stratified into layers referred to as the D, E, and F-regions with the D-region occurring at the base of the ionosphere, followed by the E-region, and then the F-region for altitudes above 150 km. Complex current systems occurring within the ionosphere can result in charge accumulation and the development of polarization electric fields. In the F-region ionosphere, electric fields cause the plasma to drift in a direction perpendicular to both the applied electric field (E) and the Earth’s background magnetic field (B). The E×B plasma drifts are the main driver of plasma transport perpendicular to magnetic field lines, and are an important parameter for controlling the distribution of plasma at low latitudes. A comprehensive understanding of the equatorial E × B plasma drifts can improve space weather forecasting which can positively impact radio-based communication system, such as GPS, that rely on radio waves that traverse the ionosphere. This study is partitioned into two parts and analyzes the variability of equatorial F-region plasma drifts. Focus and attention is given to the height variation of the drifts. The first part of this dissertation is an experimental study that utilizes long-term observations of the equatorial plasma drifts made by the incoherent scatter radar (ISR) at the Jicamarca Radio Observatory to derive local time versus height profiles of the mean plasma drifts for different season and for different levels of solar activity. Additional analysis uses day-to-day altitude profiles to determine the magnitude and variability of height gradients in the vertical plasma drifts. The second part of this study focuses on a modeling approach to analyze and improve our understanding of the plasma drifts. This analysis includes an effort to develop an empirical model of the geomagentically quiet-time vertical plasma drifts using the random forest machine learning algorithm that is trained and validated using Jicamarca ISR observations. We also develop and utilize numerical physics-based models that rely on a two-dimensional field line integrated description of the electrodynamics in the low-latitude ionosphere. These models are used to analyze the relative contribution of various sources on the development of equatorial plasma drifts. Additionally, we evaluate the ability of widely used climatological models (IRI, NRLMSISE, HWM, IGRF) of the ionosphere and thermosphere to produce a realistic morphology of equatorial F-region plasma drifts.