GRAPES的积云对流参数化方案性能评估及其改进试验

The Evaluation of Cumulus Parameterization Schemes in GRAPES Model and Its Improved Experiments

利用GRAPES(Global/Rcgional Assimilation and Prediction System)单柱模式(Single Column Mode1,SCM).采用GCSS WG4第三次个例资料,对BMJ、SAS和KFeta三种积云参数化方案进行了数值试验和诊断分析,得到如下结论:BMJ和KFeta方案都能较好地模拟出与观测相符的降水,而SAS则相对较差:BMJ方案在对流层中高层位温误差较小,低层偏冷严重,同时该方案具有较强的水汽向上输送能力,易造成低层偏干,中高层偏湿,因此其调整的大气层结过于稳定;KFeta方案倾向于造成低层偏冷偏湿,但低层偏冷幅度相对于其他方案较小,在对流层高层则由于对流穿透过强导致严重偏冷。针对KFeta方案对流穿透过强的问题,本文提出了一种新的对其垂直速度方程进行修改的方案,并且考察了Anderson等提出的修改流出层方案。数值试验表明,这两种修改都能有效地减小高层冷误差;综合来看,本文提出的修改方案的预报效果更令人满意。

By using the GRAPES （Global/Regional Assimilation and Prediction Enhanced System） Single Column Model and the GCSS WG4 Case 3 data, the numerical experiments were conducted to evaluate the cumulus parameterization schemes, such as BMJ, SAS and KFeta. The results show that BMJ and KFeta can simulate the precipitation that consistents with the observation, while SAS is relatively poor. The po- tential temperature errors of the middle and upper troposphere simulated by BMJ are smaller, but cool bias of the lower troposphere is serious, meanwhile, it has stronger ability to transport water vapor upward which leads to the lower troposphere drier, middle and high troposphere wetter, so that the atmosphere adiusted by BMJ is too stable. KFeta has a trend to be cooler and wetter at lower troposphere and mainly produces cold bias, but the magnitude of lower troposphere is smaller compared to other schemes, at upper levels serious cool bias is caused by excessive overshoot. In order to solve the problem of KFeta excessive overshoot, this paper proposes a new modified scheme in which the vertical velocity equation is modified, and the modified scheme proposed by Anderson et al. also is examined. Numerical experiments show that both modified schemes can reduce high-level cold bias effectively~ In general, the new modified scheme is more satisfactory.