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 from prior models in that it considers fluctuations in vibrationally excited hydroxyl populations [OH(ν)] instead of fluctuations in the production rate of OH(ν). Two types of correction terms to the latter class of models are found, one involving advection of excited‐state populations by the gravity wave and one involving quenching of OH(ν) by collisions with perturber molecules. Effects of these additional terms are expressed in terms of the so‐called Krassovsky ratio η, which relates relative fluctuations in the column intensity measured by a passive optical instrument to relative fluctuations in the ambient temperature. The extra wave advection term is found to be unimportant under typical conditions, but quenching is important and has two major effects: (1) It makes η a vibrational‐level‐dependent quantity, and (2) it can lower η by more than 50% depending on the wave period. A typical range for η over a reasonably chosen range of wave parameters was found to be from less than 1 up to 9. The measuring instrument was also explicitly considered in the model formulation. Instead of simply assuming that the instrument measured the brightness‐weighted temperature, as is commonly done in gravity wave response models, two common instruments for determining temperature from passive column‐integrated measurements 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‐resolution instrument, such as a Fabry‐Pérot interferometer, which uses the Doppler width of a single line to infer the temperature (the Doppler temperature). For gravity waves with large phase velocity (large‐scale waves), calculations by both of these methods are found to be generally in agreement with each other and with the brightness‐weighted temperature. However, for gravity waves with small phase velocity (small‐scale waves) the two realistic simulations can differ from simulations using the brightness‐weighted temperature by as much as 35%. The effect of vertical standing waves is considered by modifying the Hines model to include a rigid ground boundary. It is found that the standing waves have a profound effect on the phase of the gravity wave response. Values of η generated from the model are compared with published ground‐based OH Meinel measurements of a quasi‐sinusoidal short‐period gravity wave by Taylor et al. (1991) from Sacramento Peak, New Mexico, at 15° elevation, as well as with the Svalbard polar‐night data of Vi...

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A quantitative study is made of the relative importance of the purely gravitationally induced compression (GIC) due to fluid particle altitude change and the actual "wave compression" which can occur at a fixed altitude in a gravity wave. The results for density, pressure, and temperature variations show the following: (1) the GIC effects predominate (>95%) for v/c <20%, where v is the horizontal phase velocity and where very simple formulas can be obtained; (2) the relative importance depends strongly on frequency for wave periods less than 10 min but becomes totally independent of frequency for periods greater than 20 min; and (3) the temperature measurements can be quickly converted to height variations wherever the GIC effect predominates; in general, the conversion is equivalent to the adiabatic lapse rate, i.e., a 10 ø temperature variation corresponds to a height change of I km. In addition, the total kinetic energy density can be simply expressed in terms of height variation and, whenever the GIC effects predominate, can be very easily obtained from temperature measurements. An interesting by-product has been that for waves of small horizontal phase speed, the total wave kinetic energy at any frequency is equal to the kinetic energy of the natural (Brunt) oscillation of an air parcel with the same vertical displacement. •HIITY VAIl. I'llIra O.Z.I:. • ß . ß . ß ß ß .oo o'.;o 0'.40 o'..o "O':oo 40 --ø•."0 o'.oo v/c v/c ß ß . ß ß ß ß ß ß ß

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The question of whether a linear gravity wave will give rise to nonlinear effects in ground-based airglow observations is important for the proper interpretation of gravity wave dynamics. In this paper we obtain a closed form solution for the integrated airglow response to a linear gravity wave, containing all the higher-order nonlinear response terms. A comparison is made to the linear response, and the higher orders are seen to be significant. In addition, the wave-induced airglow intensity fluctuations are shown to be much greater than the corresponding major species density fluctuations. 14,141