A simple parameterization of the generation of gravity waves by deep tropical convection

In general, gravity waves have temporal and spatial scales that cannot be resolved in current General Circulation Models (GCMs). Without a parameterization of the effects of these waves, GCMs produce a modeled mean circulation which does not match observations. Such a parameterization should consist of two distinct parts. The first part is the source parameterization, where known features of the resolved flow are used to determine a spectrum of gravity waves at their source. The second part is the drag parameterization, which relates properties of the source spectrum to a tendency on the resolved flow. There are a number of sources of gravity waves, and these sources must be well understood in order to develop accurate source parameterizations. Deep convection is one of these sources, and it is the characterization of this source which is the focus of this study.

In this study, a number of cloud-resolving model calculations of deep tropical convection are used to examine the gravity-wave source characteristics of convective clouds. The primary difference between the calculations is the tropospheric wind shear of the background environment. These calculations show that tropospheric wind shear broadens the source spectrum, and Doppler shifts the spectrum with respect to the ground. These ideas are used to develop a simple parameterization of the source of the gravity waves, which could be used in a GCM.