| One of the most interesting current problems in the aeronomy of the mesosphere is the origin of sporadic Na (Na{dollar}sb{lcub}rm s{rcub}{dollar}) layers. The characteristics of the 43 Na{dollar}sb{lcub}rm s{rcub}{dollar} layers observed by the airborne Na density and the Haleakala Na wind/temperature lidars during the ALOHA/ANLC-93 campaigns are summarized. In particular, the relationship of formation of the low-latitude Na{dollar}sb{lcub}rm s{rcub}{dollar} layers to the wind and temperature structure is explored.; Gravity waves are the primary source of mesoscale fluctuations throughout the atmosphere. The effects of different source characteristics and horizontal anisotropies in the wave fields on the gravity wave spectra observed in the mesosphere are explored. The predictions of two leading gravity wave spectral models are tested using high-resolution airborne lidar data acquired during ALOHA-93.; Finally, a new gravity wave spectral model is developed. We employ more realistic models of the source spectra and diffusive filtering theory (DFT) to model the one-dimensional and two-dimensional spectra of horizontal and vertical winds, atmospheric density, and temperature. Although more complicated, this new DFT model apparently overcomes the discrepancies between some recent observations and the existing DFT model predictions. Airglow and Na-layer parameter spectra are important because they can be used to characterize the small vertical wave number region of the wave spectrum, which is relatively unaffected by dissipation. The new DFT model is used to model the horizontal wave number spectra of OH- and Na-layer parameters. The model spectra are compared with extensive lidar, balloon, and airglow imager observations obtained at a variety of sites and altitudes during the past decade. |
