中文摘要：

为了更好的了解暴雨发生的机制且为未来预报奠定基础，需要对暴雨天气过程进行诊断分析。通过利用自动站降水观测资料、台站探空资料和NCEP逐6小时再分析资料，总结分析了成都地区2011年7月03至04日特大暴雨天气过程的环流背景和主要影响系统，并对相关物理量进行了诊断分析，结果表明：（1）这次降雨主要是在高空副高的突然加强西伸、低空西南急流的水汽输送和本地积聚的不稳定能量与弱冷空气侵入共同作用下产生的。（2）暴雨开始前，成都地区位于高空水汽通量散度梯度大值区北侧的辐散区。随着暴雨发展，水汽通量散度梯度区向北移动。（3）水汽通量散度正负临界值区和湿位涡对于本次降水落区的预报有较好的指示意义。在强降水区域，低层湿位涡的垂直正压项为明显的正值中心，斜压项为梯度大值区，斜压性很强。（4）风场在850hPa等压面和低层oe=325K（大约750hPa）等熵面上均表现为气旋式弯曲，有利于强降水的发生。

英文摘要：

In order to know better about the occurrence mechanism of rainstorm and make benefits for future forecast- ing, it is necessary to do diagnostic analysis of rainstorms. Based on the observational data of precipitation of auto- matic stations, the data of sounding stations and daily grid reanalyzed data from NCEP/NCAR at 00：00 （U TC）, 06 ： 00,12 ： 00, and 18 ： 00, an extraordinary rainstorm occurred in Chengdu region from July 3rd 2011 to July 4th 2011 has been analyzed. Its circulation background and main influence systems had been summarized. A diagnos- tic analyses had also been done for some related physical quantities in this synoptic process. The findings reveal that： （ 1 ） In the upper air, the Pacific subtropical high suddenly strengthened and moved toward west; in the low level, the southwest jet stream conveyed water vapor into Chengdu region, in the locality, there was an accumulation of unsta- ble energy and a invaded weak cold air. All these observational results worked together and caused this rainstorm. （2） Before the start of the rainstorm, Chengdu region is located in the area of divergence that lied in the north of the big value area of moisture flux divergence grads. With the development of this rainstorm, the area of moisture flux diver- gence grads been northward moved. （3）The critical area of positive and negative value of moisture flux divergence and moist potential vorticity had a preferably indicative meaning for forecasting the rainfall zone. In the heavy rain zone, MPV1 had an obvious positive value center in the low area, MPV2 had a big value of grads, itsbaroclinicity is very strong. （4）The wind contrarotated on the 850 hPa constant pressure surface and a isentropic surface （0e = 325K, about 750hPa）, this is good to cause heavy precipitation.