A Full-Wave Investigation of the Use of a 'Cancellation Factor' in GW-Airglow Interaction Studies

Atmospheric gravity waves (GWs) perturb minor species involved in the chemical reactions of airglow emissions in the mesopause region of the earth's atmosphere. The so-called 'Cancellation Factor' (CF) is defined as a transfer function relating the amplitude of airglow brightness fluctuation to the amplitude of GW-induced fluctuation in temperature [Swenson and Gardner, 1998]. This transfer factor can be used to determine GW fluxes and the forcing effects of GWs on the mean state through airglow observations, because GW fluxes are proportional to the square of GW amplitude. Numerical models [Walterscheid et al., 1987; Schubert et al., 1991] have previously shown that the airglow relative brightness fluctuation can be much larger than the brightness-weighted relative temperature fluctuation (that is, Krassovsky's ratio is much greater than 1). Analytical expressions of the CF in the OH nightglow were derived by Swenson and Gardner [1998] and later used by Swenson and Liu [1998]. We introduce the full-wave model [Hickey et al., 1997, 1998] describing GW propagation in a non-isothermal, windy, and viscous atmosphere (combined with the chemical reaction scheme for the OH (8, 3) Meinel emission) to derive fluctuations in the OH nightglow from which an equivalent CF is calculated. Extensive comparisons between our CF and that of Swenson and colleagues show under what atmospheric conditions and which range of GW parameters the CF would be expected to provide a good measure of GW amplitude. This thesis consists of four chapters that deal with the calculations and comparisons of the CFs in the OH nightglow from both the analytical and numerical models under various atmospheric conditions. In the first chapter the general subject of internal GWs is introduced for the non-specialist of this field. It reviews the historical theory and observation of atmospheric GWs, and also emphasizes the role of atmospheric GWs in