GRAVITY-WAVE ACTIVITY IN THE UPPER MESOSPHERE OVER URBANA, ILLINOIS -LIDAR OBSERVATIONS AND ANALYSIS OF GRAVITY-WAVE PROPAGATION MODELS

We analyze 375 h of Na Wind/Temperature lidar measurements of the meso pause region (approximate to 80-105 km) Na density and temperature pro files on 57 nights distributed over 2 yr at Urbana, Illinois. These ob servations yield a high-resolution seasonal data set of gravity wave a ctivity in the upper mesosphere. From this data, we present measuremen ts of the Brunt-Vaisala period, the relative atmospheric density pertu rbations and their spectra, and the parameters of 143 quasi-monochroma tic gravity waves. The direct measurement of the Brunt-Vaisala period allows accurate calculation of the horizontal velocity perturbations a nd vertical displacement perturbations from the density measurements. The horizontal velocity and vertical displacement vertical wave number spectrum magnitudes and indices show considerable seasonal and nightl y variability. The gravity wave amplitudes, wavelengths, and observed periods exhibit systematic relationships similar to those found in pre vious studies, and are consistent with the MU radar measurements of in trinsic gravity wave parameters. Here, we present a detailed analysis of the observations in terms of Diffusive-Filtering Theory models of g ravity wave propagation. The magnitudes of the vertical wave number sp ectrum, the form of the joint vertical wave number and frequency spect rum, and the systematic relationships between the monochromatic gravit y wave parameters are consistent with the Diffusive-Filtering model We compare these results with a variety of radar, lidar, and airglow obs ervations from other sites. This observational study suggests that the complex nonlinear interactions of the gravity wave field may be model ed successfully as a diffusive damping process, where the effective di ffusivity is a function of the total wave variance. Copyright (C) 1996 Elsevier Science Ltd