Towards a physically based gravity wave source parameterization in a general circulation model

Middle atmospheric general circulation models (GCMs) must employ a parameterization for small-scale gravity waves (GWs). Such parameterizations typically make very simple assumptions about gravity wave sources, such as uniform distribution in space and time, or an arbitrarily specified GW source function. Here we present a configuration of the Whole Atmosphere Community Climate Model (WACCM) that replaces the arbitrarily specified GW source spectrum with GW source parameterizations. For the non-orographic wave sources we use a frontal system and convective GW source parameterization. These parameterizations link GW generation to tropospheric quantities calculated by the GCM, and hence provide a model consistent GW representation. This is a first GCM attempt to simulate middle atmospheric climate without any arbitrary source spectra. We show here that, with the new GW source parameterization, a reasonable middle atmospheric circulation can be obtained and the middle atmospheric circulation is better in several respects than that generated by a typical GW source specification. In particular, the interannual NH stratospheric variability is significantly improved as a result of the source oriented GW parameterization. We also show that the addition of a parameterization to estimate mountain stress due to unresolved orography has a large effect on the frequency of stratospheric sudden warmings in the NH stratosphere by changing the propagation of stationary planetary waves into the polar vortex.