Date of Award
Doctor of Philosophy (PhD)
Aerospace Engineering Sciences
Delores J. Knipp
This work focuses on determining how effectively the upper atmosphere, as a medium, transmits the influence of an electric field into differential charge motion (current). This effect is called conductivity. Conductivity modulates height-specific energy deposition in the ionosphere and thermosphere, and is therefore critical to the study of the Earth space environment. The key to the improvements presented in this dissertation is a complex systems approach through which cutting-edge mathematical tools and computational techniques are utilized to improve modeling and understanding of conductivity. These improvements replace limiting assumptions in conductivity modeling (Maxwellian particle energy distribution and thin-shell conductance approximation) that have existed for nearly three decades. My new computational methods permit the first global height-specific views of how solar and magnetospheric energy influence the dynamics of the ionosphere and thermosphere. This dissertation promotes much more effective and efficient use of under-used geospace observations in data assimilation and forecasting. The outcome is significantly improved conductance and conductivity modeling capabilities that underpin a system science approach to understanding geospace interactions at smaller scales and higher resolution.
This work has four facets, each addressing a limitation in the current state of conductivity modeling: 1) characterization of high-latitude particle precipitation and its combination with the effects of solar ionization; 2) creation of the conductivity model; 3) identification of the characteristic features of the ionospheric conductivity and capturing these features in a covariance model; and 4) creation of a means to estimate the dynamic global distribution of conductivity via optimal interpolation. The next step, which is explored in this dissertation, is three-dimensional, global estimation of conductivity. The engineering application of this work is in the realm of satellite drag, which is the aspect of low Earth satellite motion most affected by upper atmospheric energy deposition. A parameterized version of the calculations supporting this effort has been made freely available for scientific use.
McGranaghan, Ryan Michael, "Determining Global Ionospheric Conductivity in the Satellite and Data Assimilation Age and Assessing its Influence on the Magnetosphere-Ionosphere-Thermosphere System" (2016). Aerospace Engineering Sciences Graduate Theses & Dissertations. 134.