Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Kristine M. Larson

Second Advisor

Jeffrey M. Forbes

Third Advisor

Arthur D. Richmond

Abstract

The role of different mechanisms for generating periodic variability in the ionosphere and plasmasphere is studied in this dissertation. The impact of vertically propagating waves of lower atmospheric origin on introducing periodic spatial and temporal variability in the ionosphere and plasmasphere is first investigated. This is comprised of several different aspects. Initial focus is on the seasonal, local time, and altitude dependence of longitude variations due to nonmigrating tides in the F-region and topside ionosphere/plasmasphere using a combination of observations and numerical models. This is facilitated by the development of a new method for mitigating the effect of multipath on low-Earth orbit (LEO) satellite Global Positioning System (GPS) observations. The impact of large-scale changes in tropospheric convection due to the El-Nino Southern Oscillation on the ionosphere is also explored observationally. The influence of nonmigrating tides on the global ionosphere is revealed through study of the longitude variations in the solar quiet current system. Periodic temporal variability in the ionosphere due to planetary waves originating in the lower atmosphere is also investigated. The response of the global ionosphere to the quasi-16 day planetary wave is first presented. This is followed by observational evidence demonstrating that the nonlinear interaction between planetary waves and tides is the primary mechanism responsible for low-latitude ionospheric variability during sudden stratospheric warmings. Periodic temporal variability in the ionosphere and plasmasphere of solar origin is also studied. During the declining phase of solar cycle 23, near-Earth geospace was routinely disturbed due to high-speed solar wind streams emanating from solar coronal holes. The nature of the coronal holes was such that the Earth's upper atmosphere exhibited periodic behavior due to recurrent geomagnetic activity. A study of the latitude and local time response of the ionosphere to recurrent geomagnetic activity is performed herein. A method for estimating the location of the plasmapause from LEO GPS observations is also developed and applied to study periodic oscillations in the plasmapause.

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