Extended Abstract

PECS grow. The evolution of meso-scale PECS relates well to the evolution of positive vortex belt.The meso-scale PECS cloud cluster develops strongly because of the strong vertical motion caused bythe vertical development of the nearby vortex belt. And it will be weaken or disappear when the vortexbelt inclines, which results in the vertical motion weakening, and the related rain terminates at thesame time.The low-level moisture and warm instability energy accumulation provided the energy fordevelop of the PECS. PECS and the heavy rainfall area is in the high value area of K>34℃, theheavy rain center moving towards as similar as the big value of K>36℃. the helicity coupled thevertical velocity with vertical vorticity, which shows effectively the potential instability happen. Overthe rainfall area ,the middle-low level is the positive helicity area, that the positive value center reach8×10 -6 m/s 2 near the 600 hPa. The up level is the negative helicity area ,which the value center reach-5×10 -6 m/s 2 . The occurrence and development of the heavy rainfall and PECS is in correspondencesimilarly with helicity space distribution.Fig 4. vertical section along 119ºE of vorticity at 08:00 5th July fig5 helicity on 700hPa at 02:00 5 th July in 20035. Conclusions(1)The PECS causing the JiangSu heavy rainfall is made up of many MβEC clouds whichcorresponding to the low-level shear line, and lining along the direction from southwest to northeast.And new clouds are born and back-building which have merged into PECS. The distribution anddirection had correspondence with shear line in low level.(2) The heavy rainfall areas matched with TBB34, the heavy rain centermoving towards as similar as the big value of K>36 . The helicity coupled the vertical velocity withvertical vorticity ,which shows effectively the potential instability happen. The occurrence anddevelopment of the heavy rainfall and PECS is in correspondence similarly with helicity spacedistribution.3-445-