The Forming Conditions and Characteristics of MCSs in an Atypical Heavy Rainstorm Process

Using a variety of data to analyze MCSs in the heavy rainstorm of the 3rd to 4th June 2014，the results showed that the MCSs display a multi－ scale feature and diverse structure，namely that there were middle β－ MCSs and γ－ MCSs in the middle α－ scale MCSs，and displayed the"oval"type and the"ribbon"type，old convective clouds combined with each other to induce new convection was a distinctive feature．According to the time evolution，MCSs activity roughly divided into two phases，the first phase activity caused the heavy rainstorm in southern and northeastern of Sichuan basin，the second time phase activity caused the heavy rain in south and west of the basin．Analyzing the cause of MCSs showed that the development of MCSs have close relation with the 850hPa basin inverted trough and warm，moist southerly wind，because the precipitation system of the middle troposphere was not typical，850hPa trough ，moist－hot environment of near the Jet and unstable stratification provided favorable condition for the convection，such as greater CAPE values and the humidity structure of upper drylower wet，K index was above 36℃ ，LI index was negative，and the wet Q vector divergence was negative，the sequence physical variations were important factors to trigger MCSs growth．