Parameterization of Generalized Cloud Overlap for Radiative Calculations in General Circulation Models

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Abstract
New radiative parameterizations have been developed for the National Center for Atmospheric Research (NCAR) Community Atmospheric Model (CAM). The CAM is the next version of the NCAR Community Climate Model (CCM). This paper describes the generalized treatment of vertical cloud overlap in the radiative calculations. The new parameterizations compute the shortwave and longwave fluxes and heating rates for random overlap, maximum overlap, or an arbitrary combination of maximum and random overlap. The specification of the type of overlap is identical for the two bands, and it is completely separated from the radiative parameterizations. In the prototype of CAM (CAM 0.1), adjacent cloud layers are maximally overlapped and groups of clouds separated by cloud-free layers are randomly overlapped. The introduction of the generalized overlap assumptions permits more realistic treatments of cloud–radiative interactions. The parameterizations are based upon representations of the radiative transfer equation... Abstract New radiative parameterizations have been developed for the National Center for Atmospheric Research (NCAR) Community Atmospheric Model (CAM). The CAM is the next version of the NCAR Community Climate Model (CCM). This paper describes the generalized treatment of vertical cloud overlap in the radiative calculations. The new parameterizations compute the shortwave and longwave fluxes and heating rates for random overlap, maximum overlap, or an arbitrary combination of maximum and random overlap. The specification of the type of overlap is identical for the two bands, and it is completely separated from the radiative parameterizations. In the prototype of CAM (CAM 0.1), adjacent cloud layers are maximally overlapped and groups of clouds separated by cloud-free layers are randomly overlapped. The introduction of the generalized overlap assumptions permits more realistic treatments of cloud–radiative interactions. The parameterizations are based upon representations of the radiative transfer equation...