Description of NCAR Community Climate Model (CCM0B)

This report presents the details of the governing equations, physical parameterizations and numerical algorithms defining the version of the NCAR Community Climate Model designated CCMOB. The presentation is designed to follow the flow of the model code. It is NCAR's intention that this model provide the NCAR and university research community with a basic climate model having more emphasis on documentation and reliability than on the most recent physical embellishments. An earlier version of the NCAR Community Climate Model (designated CCMOA) based on the Australian spectral model developed by W. Bourke, B. McAvaney, K. Puri and R. Thurling (Bourke et al., 1977, McAvaney, et al., 1978) was described in Washington (1982). That model was adapted to the NCAR computers by K. Puri (Australian Numerical Meteorological Research Centre) during an extended visit and subsequently modified by E. Pitcher (University of Miami) and R. Malone (Los Alamos/DOE) to adopt more efficient Fourier transform routines and the improved radiation/cloudiness parameterizations of Ramanathan and Dickinson. The radiation and cloud models were subsequently revised to their CCMOA versions by Ramanathan. Results of January and July simulations produced by CCMOA are presented by Pitcher et al. (1983). The response of the model to refinements in the radiative processes is described by Ramanathan et al. (1983). An important broadening of the concept of the NCAR community model occurred in late 1981 with NCAR's decision to utilize the same basic code for global forecast studies (both medium- and long-range) as well as for climate simulations. Economy and increased efficiency could then be achieved by documenting and maintaining only one set of codes.