Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Jeffrey M. Forbes

Second Advisor

Maura E. Hagan

Third Advisor

Scott E. Palo

Fourth Advisor

Cora E. Randall

Fifth Advisor

Jeffrey P. Thayer

Abstract

Atmospheric tides are vertically-propagating waves generated in the lower and middle atmosphere that are widely known to affect the dynamics and electrodynamics of the ionosphere-thermosphere (IT) system. The tidal spectrum evolves with height due to wave-mean flow, wave-wave, and wave-plasma interactions, leading to the tidal spectrum observed by ground- and space-based observing platforms in the IT. Some of these observations and prior theoretical work suggest that non-linear interactions may produce important effects. However, one can only speculate about how non-linear tidal interactions and their various generation mechanisms might result in mean state, spatial, and temporal variations in the IT system based on prior work. Through numerical experiments performed with the National Center for Atmospheric Research Thermosphere General Circulation Models, this work seeks to quantify and understand how non-linear tidal interactions affect the IT system.

The main results to emerge from this study are as follows: (1) Interaction between the zonally-symmetric solar-driven circulation and the longitude-dependent ionospheric magneto-plasma produce non-migrating atmospheric tides that reconcile existing data-model disparities, mainly under solar maximum conditions; (2) Dissipating tides of lower atmospheric origin act to alter the pressure gradient force via the eddy heat transport causing zonal-mean wind differences of up to 30 m/s in the dynamo region; (3) Variations of up to 30 K in zonal-mean temperatures of the IT between solar minimum and maximum result from a combination of net eddy heat transport effects and tidal modulation of net nitric oxide cooling; (4) The net transport of atomic oxygen produced by dissipating tides is shown to significantly contribute to atomic oxygen changes in the IT; (5) Measurable solar cycle variations in electron density in the F-region result from tidally driven net changes in the major constituents of the thermosphere. The major computational results from this work will provide additional insight into current and future tidal diagnostics and related non-linear processes observed from a range of ground-based and space-based platforms.

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