The Colorado State University general circulation model (GCM) has been dramatically changed in the last few years. The previous model’s latitude-longitude grid, with "C"-grid staggering of mass, zonal and meridional wind, was replaced by a geodesic grid in which mass, vorticity and divergence are predicted on an unstaggered "Z"-grid. In addition, we have reformulated the vertical structure of the model. We have moved from the sigma-coordinate with Lorenz staggering to a hybrid sigma-theta coordinate with Charney-Phillips staggering. Such a hybrid coordinate is constructed so that it will quickly transition from terrain-following sigma-coordinate to potential temperature with increasing height, so that the advantages of the isentropic-coordinate are realized through most of the model atmosphere.
We have coupled the new dynamics to the CSU physics package. Cumulus convection is parameterized following the Arakawa-Schubert approach with a prognostic closure and multiple cloud-base levels. The stratiform cloud parameterization involves prediction of four condensed-water species in addition to water vapor. The PBL parameterization combines the effect of large convective and small diffusive eddies to determine the turbulent fluxes in a multi-layer framework.
We will show numerical results from both dry (without physics) and aquaplanet simulations.