Abstract:Based on the surface dense automatic station data, Doppler radar data and NCEP/NCAR reanalysis data, the strong convective weather occurring over Jiangsu and Anhui Provinces on April 28, 2015 under the background of cold vortex was analyzed. Moreover, the structure characteristics, formation and maintenance mechanism of the supercell storm with long life cycle, which led to the regional hail in this weather process, were also significantly studied. The results showed that the formation of the northerly jet at the back of cold vortex and cold advection which was carried to the south promoted the development of conditional unstable stratification and deep vertical wind shear, providing a favorable environment for the occurrence of severe convective weather. Surface mesoscale depression and the accompanied convergence line were one kind of the triggering mechanisms. Supercell storm with long life cycle occurred in the middle troposphere and had highly organized dynamic structure at its mature stage. The storm had the significant rotation characteristics, especially in middle layer. The middle and low layer of the storm corresponded with deep convergence zone, while the top of the storm presented obvious divergence feature. Such veritical distribution of divergence field enhanced the intensity of rising flow within the storm and the warm, humid flow in the low level of the storm, making the abundant water vapor in low level transported into the storm, so the convective storm increased vertically and developed intensively. The top height of the storm and the centroid height showed features of wave motion before and after the hail occurring. The hail happened at the rapid descending stage of the above two heights, and the centroid height had more obvious descending trend. The maintenance of supercell storm was related to the constant southerly cold advection in the middle troposphere, the strong vertical wind shear and rotation feature inside the storm.