一次皖北地区台风远距离特大暴雨预报失败原因分析

Analysizing the cause of a failure rainstorm forecast in northern Anhui

利用ECMWF、NCEP/NCAR等多家数值预报产品、ERA-Interim再分析资料以及卫星观测资料,并结合HYSPLIT轨迹模式对2011年发生在皖北的一次特大暴雨进行了分析,深入探讨了此次暴雨预报失败的原因。分析结果表明,此次暴雨为一次台风远距离降水;台风和副热带高压的外围环流为此次降水提供了充足的水汽输入;西风槽冷空气入侵也是产生这次降水的重要原因。各业务模式对此次降水预报失败的主要原因在于未能准确预报出台风和副热带高压环流的水汽和热量输送;同时,对西风槽位置的预报偏差也是预报失败的原因之一。结果指出,当有强台风靠近我国的时候,需要考虑台风环流与其他天气系统相互作用进而引发强降水的可能。

This study investigated the possible cause for a poor forecast of an extremely heavy rainfall in northern Anhui Province in 2011. The data used in this study included the numerical model output from different agencies（e.g., ECMWF,NCEP/NCAR）, ERA-Interim Re-Analysis from ECMWF, and satellite observations. Besides, the HYSPLIT trajectory model was employed to find the pathway of the water vapor in this rainfall event. The results showed that the heavy rainfall was closely related to a tropical cyclone（TC） far away. The peripheral circulation of TC, together with that of subtropical high, supplied abundant water vapor in the rainfall, which was triggered by the cold-air intrusion in front of the upper-level westerly trough. The failure forecast for this heavy rainfall by most operational models was mainly attributed to the inaccurate prediction of the water vapor and heat movement driven by TC and subtropical high pressure. Besides, the error in the prediction of the westerly-trough position also contributed to the poor forecast. These results indicated that when a strong TC is approaching, it is necessary to consider the potential extreme rainfall induced by the interaction between TC and other local systems.