Date of Award

Spring 11-22-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Jeffrey P. Thayer

Second Advisor

Jeffrey Forbes

Third Advisor

Delores Knipp

Fourth Advisor

Fran Bagenal

Fifth Advisor

Wenbin Wang

Abstract

Plasma-neutral interactions play an integral role in governing the dynamics and energy of an upper atmosphere. In the Earth's ionosphere-thermosphere (I/T) region, these interactions can produce significant structure in neutral temperature, winds, mass density, and composition. External sources of momentum and energy that directly affect these properties of the upper atmosphere have been extensively investigated, but these investigations are not sufficient to fully describe thermosphere phenomenology. Considering the strong plasma-neutral coupling in the I/T region, an internal and indirect energy mechanism, or a feedback exchange between hydrodynamics and thermodynamics, can contribute to the resultant structure. The complex, indirect consequences of internal momentum changes on neutral gas properties have not been thoroughly assessed due to the multivariate nature of the problem and limited observations. Through the use of the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model, this thesis seeks to simulate, understand, and quantify how plasma-neutral interactions affect the energy distribution of the upper thermosphere via an indirect, dynamically induced mechanism, and to establish that this mechanism can explain the existence of thermospheric density features.

The main conclusions that stem from this dissertation are as follows: (1) Changes in the field-aligned ion drag force alter neutral temperature and mass density by means of a divergent neutral wind field, commanding the formation, local time, and solar cycle variations of the equatorial thermosphere anomaly trough; (2) Ion and viscous drag forces produce balanced motion with sustained, divergent winds that change thermal and mass density structure through adiabatic heating; (3) A boundary that delineates the lower and upper thermosphere is recognized and deemed the ``thermopause", and helium is demonstrated to be an effective dynamic tracer for a circuitous energy mechanism that is instigated by wind motion.

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The results from this thesis provide an alternate and novel perspective on energy drivers in the geospace system. Space weather hinges greatly on the interactions between the charged and neutral particles of our partially-ionized atmosphere. Understanding the momentum and energy processes that occur between these species is imperative in forecasting space weather events on Earth, and it will assist further comprehension and exploration of other planetary atmospheres.

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