Impacts of a New Solar Radiation Parameterization on the CPTEC AGCM Climatological Features

Abstract

Abstract The impacts of improved atmospheric absorption on radiative fluxes, atmospheric circulation, and hydrological cycle for long-term GCM integrations are investigated. For these runs the operational version of the Centro de Previsão de Tempo e Estudos Climáticos (CPTEC) AGCM and its enhanced version with a new solar radiation scheme are used. There is an 8% increase in the annual mean global average atmospheric absorption in the enhanced integration as compared with the operational model integration. The extra absorption is due to gases (0.5%), the water vapor continuum (1.5%), and background aerosols (6%), which were not considered in the operational solar radiation scheme. Under clear-sky conditions the enhanced model atmospheric absorption is in agreement with observations to within ±3 W m−2, while for all-sky conditions the remaining errors are related to unaccounted-for cloud absorption. There is a general warm-up of the atmosphere in the enhanced model with temperatures increasing up to ∼3 K in the troposphere and ∼5–8 K in the stratosphere, bringing the model closer to the reference values. The intensities of the tropospheric jets are reduced by 7%–8%, while that of the polar night stratospheric jet is increased by 5%–10%, reducing the model systematic error. The reduced availability of latent energy for the saturated convective processes weakens the meridional circulation and slows down the hydrological cycle. The model overestimation of December–February precipitation over the South Pacific convergence zone (SPCZ) and the South Atlantic convergence zone (SACZ) is reduced by 0.5–1.0 mm day−1, and that over the Northern Hemisphere storm-tracks region is reduced by 0.5 mm day−1. On a monthly time scale, the changes in the precipitation distribution over the SACZ are found to be much larger, ±2–3 mm day−1.