Impact of δ-Four-Stream Radiative Transfer Scheme on global climate model simulation

The impact of radiative transfer scheme on global climate model (GCM) simulation is presented in this paper by comparing the difference between δ-two-stream adding method (δ-2DDA) and adding algorithm of the δ-four-stream discrete ordinates method (δ-4DDA) radiation schemes in the Atmospheric General Circulation Model of the Beijing Climate Center (BCC_AGCM). Only consider the effects of the calculation method itself, the δ-4DDA reduces the negative shortwave cloud radiative effect (CRE) in the areas with a significant fraction of low cloud, while enhances the negative shortwave CRE in the areas with the large fraction of high cloud. For the longwave CRE, the δ-4DDA enhances the longwave CRE drastically in the regions with a significant fraction of the high cloud. The feedback of clouds results in more interesting results. The δ-4DDA produces more accurate shortwave CRE in the region over the land and ocean in the middle and high latitude areas. The longwave CRE simulated by δ-4DDA is better than that affected by δ-2DDA over the ground in Africa, South America, and Atlantic. The change of radiation scheme affects the simulation of other meteorological variables. The simulation of global humidity by δ-4DDA is improved obviously. The δ-4DDA simulates more accurate temperature in continents of the northern hemisphere and precipitation in North America, Africa, northern Indian Ocean and western Pacific. Although the improvement of every physical process is required to develop the models, implementing δ-4DDA scheme into GCM and evaluating the effect of it are necessary and meaningful.