GRAPES 全球模式浅对流过程和边界层云对低云预报的影响研究

摘要

This study develops a new cloud scheme of Global/Regional Assimilation and Rrediction System (GRARES)at 50 km spatial resolution,considering the impact of the detrainment process of shallow con-vection and boundary-layer clouds on hydrometeors water contents and cloud fraction.The purpose of this research is to improve the low-level cloud prediction of GRARES model,simulate and compare the results before and after the improvement.Besides the results are compared with observational data of the Clouds and the Earth’s Radiant Energy System (CERES)and Year of Tropical Convection (YOTC).The results show that considering the detrainment process of shallow convection and boundary-layer clouds mainly in-creases the cloud fraction and liquid hydrometeor contents of low-level cloud below 700 hRa.The improved results are closer to observation.Boundary-layer stratocumulus clouds mainly affect the clouds near the top of boundary layer and the influenced thickness is less than 200 hRa.The impact magnitude of shallow con-vection detrainment process is equivalent to the one of boundary-layer clouds,but the impact thickness is more widely in the former.Shallow convection process will have a certain impact on the low clouds from surface to the height of 700 hRa.Further research shows that due to the improvement of low-level cloud prediction,forecast of cloud radiative forcing at surface and top of atmosphere could also be improved,the increasement of low-level clouds would directly enhance cloud radiative forcing at surface.%提在 GRARES 全球模式云方案中加入浅对流卷出过程和边界层云对云水（冰）、云量的影响，改进模式低云预报，模拟比较改进前后预报结果，并与 CERES（云和地球辐射能量系统）及 YOTC（热带对流年科学计划）资料进行对比分析。结果表明：考虑浅对流卷出过程和边界层云后，主要增加了模式700 hRa 以下低云量及低云中液态水凝物含量，改进后的结果与实际观测更接近。其中边界层层积云主要影响大气边界层顶附近较薄的一层云，影响厚度不超过200 hRa，浅对流卷出过程对云水和云量大小的影响与边界层云相当，而影响厚度则更广，对地面到700 hRa 间的低云都会产生一定影响。进一步研究表明，由于低云预报的改进促进了地表和大气层顶云长短波辐射强迫的预报，云的辐射强迫得以增加。