Airglow intensity variations induced by gravity waves. Part 1. generalization of the Hines-Tarasick's theory

This study generalizes the gravity wave-airglow interaction theory of Hines and Tarasick (Planetary Space Science 35 (1987) 851). A set of equations describing the wave-induced fluctuations of temperature, line-of-sight (LOS) wind, and volume emission rate (VER) are obtained for limb observations with a photometer or interferometer. The results can also be applied to ground-based measurements. Approximations at small and large zenith angles a are considered. As a central part of the treatment, the VER variation is expressed in terms of the atmospheric density (or temperature) perturbation and the displacements parallel and perpendicular to the LOS. The relative importance of these effects is characterized by an effective scale lambda (c) of the photochemical-dynamical interactions between a wave and the airglow emission. This effective scale is shown to be similar to 33 km in the mesosphere and lower thermosphere (MLT) for emission processes of three-body reactions, and to slowly increase with increasing wave vertical scales. At small zenith angle observations, the VER variation is dominated by the effect of the vertical displacement tin geographic frame) or of the density (or temperature) perturbation for waves with vertical scales smaller or larger than lambda (c), respectively. The small-scale height H-epsilon of the emission layer may play an important role only for limb measurements. When lambda (c) > 2 piH(epsilon), the VER variation is primarily controlled by vertical wave motions for a broad spectrum of vertical scales. Comparisons with observations are presented in an accompanying paper. (C) 2000 Elsevier Science Ltd. All rights reserved.