17 December 2014

Integrating New Cloud Processes in CAM5

Summary

Researchers, including Phil Rasch at DOE’s Pacific Northwest National Laboratory, recently published work describing the new integrated cloud process representations in the Community Atmosphere Model, version 5 (CAM5). CAM5 cloud parameterizations added the following unique characteristics to previous versions: 

1)A cloud macrophysical structure with horizontally non-overlapped deep cumulus, shallow cumulus, and stratus in each grid layer; 

2)Cloud–radiation–turbulence interactions that allow CAM5 to simulate marine stratocumulus more accurately than previous model versions; 

3)A more consistent treatment of the number concentrations of stratus liquid droplets and ice crystals, with activated aerosols and detrained in-cumulus condensates as the main sources and with evaporation, sedimentation, and precipitation of stratus condensate as the main sinks; 

4)Radiatively active cumulus and snow; and

5)Improved internal consistency between cloud fraction and stratiform condensate, avoiding stratiform clouds with unrealistic condensate amounts. 

CAM5 now simulates various aerosol direct and indirect effects. This paper provides a detailed description of the cloud processes in CAM5 and outlines the differences with previous versions. The simulation analyses show that CAM5 improves upon CAM3/CAM4 in global performance as well as in physical formulation. However, several problems were also identified, which can be attributed to deficient regional tuning, remaining inconsistency between various physics parameterizations, and an incomplete treatment of some physical processes.

 

Contact
Sungsu Park
National Center for Atmospheric Research (NCAR)
Publications
Park, S, CS Bretherton, and PJ Rasch.  2014.  "Integrating Cloud Processes in the Community Atmosphere Model, Version 5."  Journal of Climate 27(18): 6821-6856, doi:10.1175/JCLI-D-14-00087.1.