The Energy Budget of the NCAR Community Climate Model: CCM3

Abstract

The energy budget of the latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is described. The energy budget at the top of the atmosphere and at the earth?s surface is compared to observational estimates. The annual mean, seasonal mean, and seasonal cycle of the energy budget are evaluated in comparison with earth radiation budget data at the top of the atmosphere and with the NCAR Ocean Model (NCOM) forcing data at the ocean?s surface. Individual terms in the energy budget are discussed. The transient response of the top-of-atmosphere radiative budget to anomalies in tropical sea surface temperature is also presented. In general, the CCM3 is in excellent agreement with ERBE data in terms of annual and seasonal means. The seasonal cycle of the top-of-atmosphere radiation budget is also in good (<10 W m?2) agreement with ERBE data. At the surface, the model shortwave flux over the oceans is too large compared to data obtained by W. G. Large and colleagues (?20?30 W m?2). It is argued that this bias is related to a model underestimate of shortwave cloud absorption. The major biases in the model are related to the position of deep convection in the tropical Pacific, summertime convective activity over land regions, and the model?s inability to realistically represent marine stratus and stratocumulus clouds. Despite these deficiencies, the model?s implied ocean heat transport is in very good agreement with the explicit ocean heat transport of the NCOM uncoupled simulations. This result is a major reason for the success of the NCAR Climate System Model.