Contrast Analysis on '010805' and '080825' Heavy Rainstorm in Shanghai

'010805' and '080825' heavy rainstorm in Shanghai are two most influential processes in the recent years.The same and different characteristics are presented by atmospheric circulation background,thermal,vapor,dynamic condition and satellite cloud images,leading to heavy rainfall.'010805' heavy rainstorm was caused by tropical depression(for short 010805TD),while '080825' heavy rainstorm was irritated by mid-latitude vortex shear,and landing typhoon NURI(0812) provided the plenty of vapor and energy for the heavy rainstorm.The two heavy rainstorm processes are affected by weak cold air from north and interactions among different air masses in middle and low latitudes play a significant role in the occurrence of heavy rainstorm.Southerly and south-east jets on the east side of slow-moving 010805TD continuously provided the vapor and energy for '010805' heavy rainstorm and maintained the strength of 010805TD.Strong southwest low-level jet existed between the north-west sides of the western Pacific subtropical high and low-level shear,which provid the vapor and energy for downstream Shanghai.Convective instability energy accumulated 24 h before the start of '010805' heavy rainstorm,but the convective instability energy rapidly accumulated 12 h before the start of '080825',whose the atmospheric convective instability is stronger.Atmosphere over Shanghai became unstable before the starting of two processes,while K index rise up more than 36 ℃.Vapor transportation started 12~24 h before the starting of the two processes.Vapor in '010805' heavy rainstorm was transported by southerly and south-east jets from East China Sea,while vapor in '080825' heavy rainstorm was transported by south-west jets from South China Sea and south-west region of China.Both of the precipitable water of atmosphere were above 60 mm in the two heavy rainstorm processes of Shanghai.Their positive vorticity and updraft gathered in very narrow area over Shanghai,as illustrated the reason why heavy rainstorm occurred only in Shanghai from one side.Convective cloud cells have the characteristics of backward transmission.It is one of the reasons that mesoscale convective cloud cells rapidly strengthen to combin with bright cloud core occurred behind weakened convective cloud cell.The combination of cloud cells is also one of the reasons that suddenly accelerate the evolvements of mesoscale convective cloud cells.