Date of Award:

5-2015

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Physics

Committee Chair(s)

Bela Fejer

Committee

Bela Fejer

Committee

Robert Schunk

Committee

Michael Taylor

Committee

Ludger Scherliess

Committee

David Geller

Abstract

In the modern world, we increasingly depend on space-based systems for our communication, positioning, and navigation systems. These systems depend on electromagnetic waves propagating through the ionosphere. The ionosphere is the medium in the upper atmosphere where, due to presence of the charged atomic and molecular particles and electrons collectively known as plasma, it influences the traveling electromagnetic waves following laws of electrodynamics. Improved models for predicting space weather conditions require improved knowledge of the drifts of these plasmas in the ionosphere. This study is focused on climatology of the altitudinal variations of these plasma drifts in the equatorial latitudes. We used vertical and zonal plasma drift data measured by Jicamarca radars from 150 km to about 600 km altitude in bimonthly bins. One of the objectives of this study is to understand the relationship between E- and F-region drifts during the daytime. The vertical drifts, in general increase with altitude in the morning hours and decrease with altitude in the afternoon. The vertical drifts change mostly linearly from E- to F-region altitudes except in the morning hours of May-June when the gradients are very small. The zonal drifts, on the other hand, show large nonlinear decrease with altitude at the lower altitudes and then slowly decrease with increasing height. We also observed occasional exceptions to these general patterns, especially in the morning hours of March-April and May-June. The E-region zonal drifts show more day-to-day variability compared to higher altitudes. The altitudinal variations during the special periods, known as sudden stratospheric warming periods, have also been studied. While the altitudinal variations do not change much for vertical drifts, the sudden stratospheric events do not seem to affect zonal drifts much.

We also presented altitudinal variations of vertical plasma drifts during late afternoon and evening time when these variations change more rapidly compared to the daytime. For the first time, we presented observations of drifts up to 2000 km altitude. We found that during the evening prereversal enhancement, the drifts increase with altitude up to the F-region peak, above which the drifts decrease with altitude until a height from where they become height independent. This transition from height-dependent to height-independent drifts seems to increase with increasing solar flux. We also addressed the relationship between the vertical and zonal plasma drifts and how the time derivatives of zonal drifts balance the altitudinal gradients of vertical plasma drifts. Neglecting these altitudinal variations would violate the curl-free condition of the electric field in the ionosphere; and thus, these variations are important to be incorporated in the present ionospheric models to improve space weather predictions.

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