Comparison and evaluation of AGCM Radiation Parameterizations in the Arctic

The performance of several shortwave and longwave radiation codes is assessed for Arctic conditions. Many of the participating models are commonly employed as atmospheric general circulation model (AGCM) parameterizations. All model input, such as atmospheric profiles of temperature, humidity and pressure, is derived from data collected during the Surface Heat Budget of the Arctic (SHEBA) field experiment. Broadband and spectral radiative fluxes observed at the surface and the top of the atmosphere are used to evaluate the codes under a variety of cases, including several clear sky days, three liquid cloud days and one ice cloud day. A line-by-line radiative transfer model is also employed to yield insight into the implementation of the codes. Many aspects of the models, such as the radiative transfer scheme, the surface albedo characterization, and the parameterized cloud and aerosol optical properties, are examined. The sensitivity of the simulated fluxes to systematic variations in cloud and aerosol properties, surface albedo and precipitable water vapor is explored.