NCAR RegCM2对1991年夏季江淮流域异常降水事件中关键物理过程的模拟能力检验

摘要

The excessively torrential rainfall over the Yangtze-Huaihe valley during the summer of 1991 is simulated with an updated version of the second generation NCAR regional climate model (RegCM2) as a case factors contributing to the generation of the anomalous rainfall. This simulation is driven by large-scale atmospheric lateral boundary conditions derived from the European Center for Medium Range Weather Forecast (ECMWF) analysis. The simulation period is May to August 1991. The model domain covers East Asia and its adjacent oceanic regions. The model resolution is 60 km × 60 km in the horizontal and 23 layers in the vertical.rnThe model can reasonably reproduce the daily precipitation events over East Asia for the summer of 1991, especially in the Yangtze-Huaihe valley where the anomalous rainfall occurred. The spatial and temporal structure of some important physical variables and processes related to the generation of the anomalous rainfall are analyzed. The time evolution of simulated upward vertical motion and horizontal convergence agrees with the five rainfall episodes over this subregion. The water vapor feeding the rainfall is mostly transported by the horizontal atmospheric motions from outside of the region rather than from local sources. The subtropical high over the western Pacific Ocean controls the progress and retreat of the summer monsoon over East Asia, and the RegCM2 can simulate the northward migration and southward retreat of subtropical high over the western Pacific Ocean. Furthermore, the model can represent the daily variation of the low level jet, which is crucial in the water vapor transport to the Yangtze-Huaihe valley.%选取1991年夏季江淮流域发生的持续性特大暴雨洪涝个例,利用NCAR第二代区域气候模式RegCM2对逐日降水过程及其关键物理因子进行了数值模拟.模式的侧边界条件由ECMWF的大尺度分析资料提供,模拟时间为1991年5-8月.模式范围包括东亚地区及相邻海域,水平分辨率为60 km×60 km,垂直方向为23层.试验结果显示,该模式能够合理地模拟出1991年夏季东亚地区的逐日降水过程,特别是在江淮流域发生的异常降水事件.对一些关键物理变量和过程时空结构的分析表明，大气垂直速度和水平散度的时间演变与江淮流域的5次降水事件一致；形成异常降水的水汽来源主要是大气的水平运动输送。西太平洋副热带高压控制着东亚夏季季风的进退，RegCM2能够模拟出西太平洋副高的南北位置移动。而且，模式能够较好地再现出对水汽输送至关重要的低空急流的逐日变化。