Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Xinzhao Chu

Second Advisor

Arthur Richmond

Abstract

By blocking extreme hazards from space and regulating radio wave propagation, the space-atmosphere interaction region (SAIR) -- our window to open space -- is essential for life on Earth and modern society. However, the physical and chemical processes governing the SAIR are not sufficiently understood due to the woefully incomplete measurements of neutral properties in this region, especially between 100 and 200 km altitude. Thermospheric Fe layers extending from ~70 to 170 km discovered by the Fe Boltzmann lidar at McMurdo, Antarctica have opened a new door to observing the neutral thermosphere and mesosphere. This thesis is aimed at revealing such new discoveries, and advancing our understanding of the thermospheric Fe layer formation, through analyzing the lidar data collected by the author in Antarctic winter and developing the first thermospheric Fe/Fe+ model.

A one-dimensional high-latitude Fe/Fe+ model based on physical and chemical first principles has been developed to quantitatively explore the source, formation and evolution of thermospheric Fe layers. We demonstrate that the observed Fe layers are produced by neutralization of converged Fe+, mainly through the direct electron-Fe+ recombination. We find that the polar electric field is capable of uplifting Fe+ ions from the main deposition region into the thermosphere, supplying the source of neutral Fe. Both gravity-wave-induced wind shears and the polar electric field can converge Fe+ layers. Vertical wind plays a key role in transporting Fe to form the observed wave structures, but horizontal divergence can largely offset the vertical convergence effects. These theoretical studies lay the foundation for exploring the thermosphere by resonance lidars.

The diurnal variations of Fe layers in the mesopause region are characterized with our lidar observations at McMurdo. A new finding is the solar effect on the Fe layer bottomside -- daytime downward extension and nighttime upward contraction. We explain qualitatively how both neutral Fe chemistry with H, O and O3 and photolysis of Fe-containing molecular species may play important roles in such Fe diurnal variations. These are entirely new results that provide direct, real-time, quantitative evidence for the influence of solar UV radiation on the chemistry and composition of the mesopause region.

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