Simulating the Arctic in the Community Climate System Model
The Arctic is a particularly challenging region to simulate accurately in a climate model, yet it is an important region because it is undergoing rapid change. In preparation for the upcoming Climate Model Inter-comparison Project (CMIP5), part of the Intergovernmental Panel on Climate Change, DOE researchers at Lawrence Berkeley National Laboratory assessed the Arctic climate in the fourth version of the Community Climate System Model (CCSM4), the version most often used in the CMIP5. An ensemble of 20th Century CCSM4 simulations was compared to a variety of reanalysis and measurement products to assess CCSM’s ability to accurately simulate the present-day Arctic atmosphere. Analyses included evaluations of surface air temperature, sea-level pressure, the atmospheric energy budget, precipitation and evaporation, cloud properties, and lower tropospheric stability. The model demonstrated the best performance in simulating surface air temperature. Errors in sea-level pressure fields were significant at certain times of year, impacting the atmospheric circulation. The model has too few clouds, and the clouds it does produce are generally too thick. Precipitation was overestimated in the Arctic and the lower atmosphere was demonstrated to be excessively stable. The results from this evaluation will help guide future model developments and in the interpretation of the CMIP5 simulations.
de Boer, G., W. Chapman, J. Kay, B. Medeiros, M. D. Shupe, S. Vavrus, and J. E. Walsh. 2011. “A Characterization of the Present-Day Arctic Atmosphere in CCSM4,” Journal of Climate. DOI: 10.1175/JCLI-D-11-00228.1.