Effects of Improved Radiative Transfer Modeling for Climate Simulations

The interaction of shortwave and infrared radiation in the atmosphere with clouds and greenhouse gases represents a complex process that contributes significantly to maintaining earth's climate system. For climate model simulations to become more accurate, it is essential that this process be modeled properly as verified by direct comparisons with observations and with results from a validated line-by-line model. For this purpose, a rapid radiative transfer model (RRTM) has been developed that reproduces the computational accuracy of a more complex line-by-line radiative transfer model (LBLRTM) (Clough and Iacono 1995) at the high speed necessary for its application within a general circulation model. We have compared RRTM longwave fluxes and cooling rates to those calculated by the National Center for Atmospheric Research's (NCAR) Community Climate Model (CCM3) radiation algorithm for both clear and cloudy conditions. We will introduce RRTM into CCM3 to establish the effect of the improved longwave radiative cooling rate profiles on the global simulation of temperature, moisture, precipitation, and the general circulation, in addition to surface and top of the atmosphere radiative fluxes.