Airglow intensity variations induced by gravity waves. Part 2: comparisonswith observations

The generalized gravity wave-airglow interaction theory presented in the fi rst paper of this two part series by Wang et al. (2001) is further develope d for comparisons with observations. As a counterpart of Krassovsky's airgl ow intensity-to-temperature ratio eta, we propose the ratio of the line-of- sight (LOS) perturbation wind to the intensity, eta (w) The behaviors of th ese ratios are determined by the intrinsic wave frequency, rather than the observed frequency. The Doppler-shifting effects are investigated and found to be quite important. For a given observed frequency, an increasing (decr easing) magnitude and phase angle of eta is generally expected, in response to the downward (upward) Doppler-shifting of the intrinsic frequencies for the waves propagating along (against) a mean flow. In a wind-temperature-s tratified atmosphere, the magnitude of eta may vary by a factor of similar to2 or more, with larger values corresponding to small-scale waves, and the phase angles may change by similar to 40-90 degrees, with larger values oc curring for either large-scale or very small-scale wave modes. For eta (w) which is proportional to 1/eta its Doppler response generally exhibits a te ndency opposite to that of eta. These ratios are also dependent on zenith a ngle theta, at which observations are made. Ln particular, theta -dependenc e of eta (w) is primarily controlled by different contributions of horizont al and vertical motions to the LOS wind. For limb scans, small-scale gravit y waves with relatively large vertical perturbation velocities are shown to play an important role in producing the observed large airglow intensity v ariations. In order to explore the importance, we simulate the green line a irglow images observed by WINDII, the WIND Imaging Interferometer on the Up per Atmosphere Research Satellite (UARS), by numerically integrating the Mi chelson equation of the instrument. The model-calculated ratios and simulat ed images are compared with realistic observations from the ground and spac e in good agreements. (C) 2000 Elsevier Science Ltd. All rights reserved.