Date of Award:

Summer 8-2017

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Physics

Advisor/Chair:

Jan J. Sojka

Abstract

Ionospheric scale height is a measure of the topside altitude dependence of electron density and is a key ionospheric parameter due to its intrinsic connection to ionospheric dynamics, plasma temperature, and composition. A longtime problem has been that information on the bottomside ionospheric profile is readily available, but the observation of the topside ionosphere is still challenging. Despite numerous data techniques to characterize the topside ionosphere, the knowledge of the behavior of the topside ionosphere and its subsequent scale heights remains insufficient. The goal of this study is to evaluate whether or not we can characterize the topside ionospheric density and temperature profiles in the event that neither temperature nor electron density are measured by using a cost-effective method.

In a simple model, the electron density in the F-region topside decreases exponentially with height. This exponential decay is mainly driven by thermal diffusive equilibrium, but also dependent on the dominant ion species, as well as other drivers during nondiffusive conditions. A scale height based on observations of the temperature can generate topside electron density profiles. While a measure of the electron density profile enables a scale height to be inferred, hence yielding temperature information.

We found a new way to represent how much total electron content (TEC) is allotted for the topside ionosphere. We then used this information to successfully determine TEC using ionosonde data containing only bottomside electron density information. For the first time, slab thickness, which is directly proportional to scale height, was found to be correlated to the peak density height and introduced as a new index, k. Ultimately, k relates electron density parameters and can be a very useful tool for describing the topside ionosphere shape and subsequently, scale height. The methodology of using cost-effective, readily available ionosonde bottomside electron density data combined with GPS TEC was discovered to be capable of inferring the topside ionosphere. This was verified by incoherent scatter radar (ISR) data, though major issues surrounding the availability of ionogram data during nighttime hours greatly limited our study, especially during diffusive equilibrium conditions. Also, significant differences were found between ISR and ionosonde-determined peak density parameters, NmF2 and hmF2, and raised concerns in how the instruments were calibrated.

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