Abstract:By using the data of conventional observation and surface automatic station observation, FY 2D and FY 2E satellite cloud images, NCEP 1°×1° FNL analysis data and EC 0.25°×0.25° fine grid model data, the evolution features of mesoscale convective system (MCS), low tropospheric wind impact on MCS development and vertical circulation structure of Meiyu front in a Meiyu heavy rainfall event that happened during 15-18 June 2015 were studied in this paper. It was found that the local heavy rainfall in south of Jiangsu Province was caused by emergence and downstream movement of a series of MCSs along synoptic scale Meiyu front and their strengthening through the positive vorticity belt in central Anhui and southern Jiangsu. There was good agreement on locations between the heavy rainfall and low level jet (LLJ) core. In vertical direction, the right side of high level jet (HLJ) was overlaid on the left front side of LLJ core resulting in obvious coupling between the two systems. During the heavy rainfall, there was both strong vertical shear in low tropospheric horizontal wind and distinct inhomogeneous distribution of upward motion in southern Jiangsu which were favorable for the enhancement of vertical vorticity and development of MCS.High vertical wind shear in low troposphere was also helpful for merging water vapor from different moisture sources along Meiyu front.The dry cold air in the north of Meiyu front moved close to the front zone through a northeast (northwest) track in low level (middle level) troposphere. And warm moisture air in the south of Meiyu front approached the front zone and went upward by a southwest way. As the warm moisture air particles approached Meiyu front zone, they turned to move eastward gradually and flowed away quickly through the pumping effect of HLJ.There was cross front motion for near surface air. The vertical secondary circulation of Meiyu front was induced by strong high level divergence and supplement and circulation of mass during the moving process of atmosphere.