Boundary-layer clouds in the Community Atmosphere Model with a unified PDF-based scheme
Authors
Peter A Bogenschutz — National Center for Atmospheric Research
Andrew Gettelman — National Center for Atmospheric Research (NCAR)
Hugh Clifton Morrison — University Corporation for Atmospheric Research
Vincent Larson — University of Wisconsin, Milwaukee
Category
Modeling
Description
This presentation describes the coupling of the Community Atmosphere Model 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 schemes 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. CAM-CLUBB especially excels in the representation of transitional cumulus under stratocumulus regimes found in the subtropical oceans. In addition, CAM-CLUBB appears to be more robust to changes in the horizontal, vertical, and temporal resolution, suggesting that CLUBB may provide a more scale-aware parameterization compared to conventional CAM5 physics. These improvements are owed in part to the more unified nature of the new turbulence scheme.