Multi-scale Observation Analysis of Extreme Heavy Rain on July 7th~11th in Sichuan Basin

Using a variety of observational data to analyze the extreme precipitation characteristics of the western Sichuan Basin occurred on July 7th to July 11 th, 2013 and local convective conditions of the heavy rain, the results showed that:(1) the continuous heavy rain includes two stages of convection and stratification stability, at early stage, convective precipitation is obvious and hour precipitation is strong, the cloud top temperature of mesoscale convective system (MCS) is low and exists cold cloud area, PPI velocity of Chengdu radar displays that there is inverse velocity region, echo thickness of values of ≥ 45 dBz was large. In the late period, stratification stability precipitation is obvious and hour precipitation is small, but the long duration, the cloud top temperature is higher, no cold cloud area and echo intensity is around 20-40 dBz, also the existence of"bull's eye"structure of Chengdu radar PPI velocity map shows that the low northeast wind is remarkable in heavy rain area. (2) the physical factors about convective precipitation converting to stratification stability precipitation mainly had relations with CAPE variation and vertical wind shear, at precipitation strengthened (weakened) period, there is (no) CAPE value and low wind speed is small (large), but upper-wind speed is high (high), the vertical wind shear is significant (not significant). (3) Under the background of weaker the low-level south wind and strong northeast wind, the convergence caused by ground cyclonic flow field not only provide water supply for the heavy rain storm, but also provides the uplift mechanism of mesoscale convergence line the trigger for precipitation, especially at poor low-moisture transport and stable stratification stage, flow cyclone near the ground becomes more and more important, so the ground cyclone flow field plays an important role in the heavy storm.