Date of Award:

5-1998

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Physics

Committee Chair(s)

Michael J. Taylor

Committee

Michael J. Taylor

Committee

William Pendleton, Jr.

Committee

Farrell W. Edwards

Abstract

Studies of internal gravity waves in the earth's upper atmosphere are of considerable interest. These waves play a very important role in the dynamics of the mesosphere and lower thermosphere (ML T) region where they can transfer large amounts of energy and momentum from the lower atmosphere via wave saturation and dissipation. In particular, small-scale short-period ( < 1 hour) waves of the type regularly recorded by all-sky nightglow imagers operated by Utah State University (USU) are known to be very important contributors. In this thesis attention is focused on a subset of small-scale wave phenomena recently discovered using such image data, the so called "frontal events." Frontal events have distinguishable characteristics from usual short-period ( < 1 hour) gravity waves. The principal characteristics are a well defined leading "front, " which exhibits a sharp change in intensity followed by a coherent wave trail (often extending from horizon to horizon) and relatively high phase speeds ( > 50ms-1) Another unusual characteristic of "frontal events" is an apparent reversal in contrast of the wave structures as imaged in the hydroxyl (OH) emission (peak altitude - 87 km) when compared with the oxygen (OJ) "green line" (557.7 nm) emission (peak altitude -96 km) that can sometimes occur. In one isolated case, observed from Haleakala, Hawaii, the bright wave crests in the OH emission appeared to propagated through a dark structureless sky, whereas in the OI emission the same waves appeared to propagate into a bright sky, leaving an apparently depleted emission in its wake. Recent theoretical studies based on noble measurements have shown that frontal events may be due to a "bore-like" intrusion that raises the OJ (557. 7 nm) layer by a few km and at the same time depresses the OH layer by a similar amount. However, studies of fronts and bores in the ML T region are exceptionally rare.

I have discovered and analyzed 16 frontal events from image data recorded at Bear Lake Observatory, Utah ( 41.6°N, 111.6°W), over the past four years. I have investigated some of their properties such as their horizontal wavelengths, horizontal phase speeds, observed periods, and their directions of motion. In addition, I have made comparative measurements of their relative intensities in the OH and OI emissions. These studies provide the first "extensive" data set on such events detailing their morphology and dynamics and should provide important information necessary for a deeper understanding of their occurrence frequency and properties.

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