The role of nonlinear processes in the generation of gravity waves by convective clouds

Convective clouds generate gravity waves and these waves are known to have important influences on the momentum budget of the middle atmosphere. Significant advances in our understanding of the wave generation process and the resultant spectrum have been achieved in the last decade using theory, models, and observations. One outcome of this understanding has been the development of a number of new parameterizations of the source spectrum of convectively generated gravity waves for use in general circulation models. These source parameterizations are ultimately based on the linear response to imposed diabatic heating. However, previous studies have shown that nonlinearities within convective clouds play an important role in defining the wave spectrum. In this study, we focus our attention on the characteristics and dynamics of these nonlinearities. In particular, a set of idealized linear and nonlinear models forced by an imposed diabatic heat source are used to explore the role of nonlinearities in the wave generation process. These simulations clearly show that the nonlinearities play the key role in the production of gravity waves that have frequencies close to the Brunt-Väisälä frequency. They also demonstrate that the fully nonlinear wave spectrum is readily reproduced using a weakly nonlinear source formulation. The implications for these results for improving gravity wave source parameterizations will also be presented.