江淮地区一次特大暴雨过程预报偏差分析

利用加密自动气象观测站资料、ERA5 再分析资料和欧洲中心 ECMWF（European Centre for Medium-Range WeatherForecasts）模式、中国气象局 CMA-MESO（China Meteorological Administration Mesoscale Model）模式产品，对 2020 年 7 月 17—18 日江淮地区一次特大暴雨过程的预报效果进行检验与分析，并对数值模式降水预报出现偏差的可能原因进行了讨论。结果表明：低涡切变和低层急流的共同影响，为强降水提供了充沛的水汽和有利的动力条件。高空干冷空气叠加在低层暖区之上形成的位势不稳定层结和垂直风切变为强降水的发生提供了不稳定条件。17日20时—19日08时CMA-MESO模式逐12 h暴雨、大暴雨以及暴雨以上量级降水的TS评分均优于ECMWF模式，但2种模式对18日08—20时暖区降水的预报结果均较差。CMA-MESO模式预报的降水区域和实况区域重叠面积的比例均显著高于ECMWF模式，预报形态也与实况更为接近。模式对冷空气强度预报偏弱造成了冷切辐合偏北，对中层湿舌的位置预报偏北，水汽强度预报偏弱，与强降水落区预报偏北相对应，可能是降水预报出现明显偏差的原因。

Study on forecast bias of an extreme heavy rainstorm process in Jiang-huai Basin

Based on the automatic meteorological observation station data，ERA5 reanalysis data，and ECMWF（European Centre forMedium-Range Weather Forecasts），CMA-MESO（China Meteorological Administration Mesoscale Model）model products，the forecast of an extreme heavy rainstorm event occurred in Jiang-huai basin during 17-18 July 2020 was verified and the possible reasons for deviations in the numerical model precipitation forecast were discussed. The results showed that the combined effects of low vortex shear and low-level jet flow provided abundant water vapor and favorable dynamic conditions for this heavy precipitation. The superposition of high-level cold air on the low-level warm area formed strong potential instability stratification and strong vertical wind shear，which provided unstable conditions for the occurrence and development of heavy precipitation. From 20：00 BT on 17 to 08：00 BT on19，CMA-MESO’s TS scores of 12 hour rainstorm，heavy rainstorm and rainstorm precipitation were better than ECMWF，but both models displayed poor precipitation forecasts in the warm zone from 08：00 BT to 20：00 BT on 18 July. The ratio of overlap areas between actual precipitation areas and predicted areas of CMA-MESO was significantly higher than that of ECMWF，and the predicted pattern of precipitation was closer to the actual situation. The weak prediction of cold air intensity by the model led to a northward convergence of cold shear，a northward prediction of the position of wet tongue in the middle layer，and a weak prediction of water vapor intensity，resulting in the significant deviation of precipitation prediction.