Coupling the Community Atmosphere Model with a Higher-Order Turbulence Closure

This presentation describes the coupling of the Community Atmosphere Model (CAM) version 5 (CAM5) with a trivariate PDF turbulence scheme, known as Cloud Layers Unified by Binormals (CLUBB). This third-order turbulence parameterization replaces the planetary boundary layer (PBL), shallow convection, and cloud macrophysics parameterizations in CAM5. The coupling of CAM with CLUBB (CAM-CLUBB) represents a more unified treatment of boundary layer and shallow convective processes which drives a single double-moment microphysics scheme. Therefore, this also leads to a more unified treatment of cloud-aerosol interactions compared to CAM5, which has separate shallow convective and stratiform microphysics parameterizations.

Results from both single-column and global simulations are presented and suggest that CAM-CLUBB can provide a better treatment of boundary layer clouds and processes, when compared to CAM5. Simulations of cumulus, stratocumulus, and transitional types of boundary layer clouds are more robust to changes of vertical and temporal resolution in CAM-CLUBB, owing to the unified nature of the new turbulence parameterization. Preliminary global simulations of CAM-CLUBB suggest promising results for unified higher-order turbulence closure schemes in general circulation models.