PHOTOCHEMICAL-DYNAMICAL MODELING OF THE MEASURED RESPONSE OF AIRGLOW TO GRAVITY-WAVES .1. BASIC MODEL FOR OH AIRGLOW

A photochemical-dynamical model for the OH Meinel airglow is developed and used to study the fluctuations in OH emission due to atmospheric gravity waves propagating through the mesosphere. The linear response of the OH Meinel emission to gravity wave perturbations is calculated assuming realistic photochemistry and gravity wave dynamics satisfying Hines (1960) isothermal windless model. The current model differs fro m prior models in that it considers fluctuations in vibrationally exci ted hydroxyl populations [OH(v)] instead of fluctuations in the produc tion rate of OH(v). Two types of correction terms to the latter class of models are found, one involving advection of excited-state populati ons by the gravity wave and one involving quenching of OH(v) by collis ions with perturber molecules. Effects of these additional terms are e xpressed in terms of the so-called Krassovsky ratio eta, which relates relative fluctuations in the column intensity measured by a passive o ptical instrument to relative fluctuations in the ambient temperature. The extra wave advection term is found to be unimportant under typica l conditions, but quenching is important and has two major effects: (1 ) It makes eta a vibrational-level-dependent quantity, and (2) it can lower eta by more than 50% depending on the wave period. Atypical rang e for eta over a reasonably chosen range of wave parameters was found to be from less than 1 up to 9. The measuring instrument was also expl icitly considered in the model formulation. Instead of simply assuming that the instrument measured the bright ness-weighted temperature, as is commonly done in gravity wave response models, two common instrume nts for determining temperature from passive column-integrated measure ments were explicitly modeled. The instruments modeled consisted of (1 ) a moderate-resolution instrument, such as a Michelson interferometer , which infers the temperature from the ratio of two rotational lines in a vibrational band (the rotational temperature) and (2) a high-reso lution instrument, such as a Fabry-Perot interferometer, which uses th e Doppler width of a single line to infer the temperature (the Doppler temperature). For gravity waves with large phase velocity (large-scal e waves), calculations by both of these methods are found to be genera lly in agreement with each other and with the brightness-weighted temp erature. However, for gravity waves with small phase velocity (small-s cale waves) the two realistic simulations can differ from simulations using the brightness-weighted temperature by as much as 35%. The effec t of vertical standing waves is considered by modifying the Hines mode l to include a rigid ground boundary. It is found that the standing wa ves have a profound effect on the phase of the gravity wave response. Values of eta generated from the model are compared with published gro und-based OH Meinel measurements of a quasi-sinusoidal short-period gr avity wave by Taylor et al. (1991) from Sacramento Peak, New Mexico, a t 15 degrees elevation, as well as with the Svalbard polar-night data of Viereck and Deehr (1989). The agreement was found to be reasonable in both amplitude and phase for standing waves.