On the importance of gravity waves in the middle atmosphere and their parameterization in general circulation models

This tutorial paper discusses the problem of parameterizing unresolved grav ity waves in general circulation models (GCMs) of the middle atmosphere. Fo r readers who are unfamiliar with middle atmosphere dynamics a review of th e basic dynamics of both the large-scale circulation and internal gravity w aves is presented. A fairly detailed and physically-based description is gi ven of several gravity wave drag (GWD) schemes that are currently employed in middle atmosphere GCMs. These include the parameterizations of McFarlane (1987), Medvedev and Klaassen (1995), and Hines (1997a,b), which are used in the Canadian Middle Atmosphere Model, as well as the parameterization of Fritts and Lu (1993), which is used in the TIME-GCM. Results from a mechan istic model and the two above mentioned GCMs are presented and discussed. T his paper is not intended as a review of all GWD parameterizations nor is i t meant as a quantitative comparison of the schemes that have been chosen. (C) 1998 Elsevier Science Ltd. All rights reserved.