A DIAGNOSTIC STUDY OF THE SOUTHERN-HEMISPHERE SUMMER CIRCULATION OF THE CCC GENERAL-CIRCULATION MODEL

The medium-scale wave regime, consisting largely of zonal wavenumbers 5-7, frequently dominates the summer Southern Hemisphere tropospheric circulation. We perform a diagnostic study of this circulation as simulated by the Canadian Climate Centre (CCC) general circulation model (GCM). The analysis of Hovmoller diagrams, space-time and zonal wavenumber spectra shows that the CCC GCM is able to simulate the observed medium-scale wave regime. The zonally averaged meridional eddy heat and momentum transports and the associated baroclinic and barotropic energy conversions are also examined. The distributions of the transports on the vertical plane agree well with the observations. After comparison with the observed December-January-February 1979 distributions, some quantitative differences remain: the heat transport is too weak aloft and too large near the surface, whereas the momentum transport tends to be too weak. The baroclinic and barotropic conversions show a maximum in the medium-scale waves. The time evolution of the Richardson number of the mean flow suggests that the medium-scale wave is due to a baroclinic instability.