Preliminary GCM Results with a New Radiation Parameterization

A new parameterization of solar and terrestrial radiation was developed and tested. The solar radiation parameterization is based on that of Lacis and Hansen (1974), but with zenith-angle-dependent surface albedoes, and revised treatments of cloudiness. The terrestrial radiation parameterization is based on the work of Chou (1984) for water vapor, Chou and Peng (1983) for carbon dioxide, and Rogers (1968) for ozone, with a new parameterization of the effects of clouds. Results obtained were compared with the new parameterizations to those obtained with the earlier parameterization described by Schlessinger (1976). Several dramatic improvements came to light. For the most part these are related to the fact that the new terrestrial radiation paramerization includes the effects of the water vapor continuum, while the earlier parameterization does not. In the moist tropical planetary boundary layer (PBL) continuum emission leads to much stronger cooling of the PBL over the oceans. Over land, however, the cooling of the PBL is significantly reduced. The latter, somewhat paradoxical result is due to the strong diurnal cycle of the continental PBL. At night the shallow continental PBL is overlain by a moist layer created by mixing during the previous afternoon. The moist upper layer acts as a radiative blanket, reducing the time-averaged radiative cooling of the continental PBL.