THE SIMULATED EARTH RADIATION BUDGET OF THE NATIONAL CENTER FOR ATMOSPHERIC RESEARCH COMMUNITY CLIMATE MODEL CCM2 AND COMPARISONS WITH THE EARTH RADIATION BUDGET EXPERIMENT (ERBE)

This study documents the Earth radiation budget as simulated by the latest version of the National Center for Atmospheric Research community climate model (CCM2). The validation of the simulated Earth radiation budget is carried out through comparison with Earth Radiation Budget Experiment (ERBE) data. The study also documents the new cloud parameterization employed by CCM2. In general, the radiation budget of CCM2 is in better agreement with the ERBE data than previous versions of the CCM. In particular, the latitudinal structure of cloud radiative forcing is much improved over CCM1. The phase of the simulated seasonal cycle in top of atmosphere radiation quantities is well represented. In the tropics the magnitude is in good agreement with the observations from ERBE. In the northern hemisphere summer the model radiative properties contain a bias. In the shortwave spectral region the clouds reflect an insufficient amount of solar radiation, while in the longwave, too much radiation is emitted to space. These biases are associated with deficiencies in the cloud optical properties, namely, cloud liquid water path and cloud effective radius specification.