NUMERICAL SIMULATION STDUY OF HAIL CLOUDPART II.MECHANISM OF HALL FORMATION AND HAIL SUPPRESSION WITH SEEDING

A detailed 3-D hail cloud numerical model and parameterization of mierophysieal processeswere described in Part Ⅰ(Hong 1999)of this study.In this part,a hail cloud occurring in Xunyiarea.Shaanxi Province on July 8,1997 is simulated by the model to analyze mechanisms of hailformation and hail suppression with seeding.The results show that 97% of hail embryos are frozendrops.The seeding experiments with AgI in terms of heights show that if the seeding is madebefore hail formation,the optimum seeding position is located in the maximum updraft area and itscenter,i.e.,AgI is seeded in the zone with high water content to be coordinated with maximumzone of the updraft.The seeding makes concentrations of graupel and frozen drop increase andtheir average mass or size decrease,so that the proportion of conversion from graupel and frozendrop into hail descends greatly,and the mass and concentration of hailstone are decreased toachieve our purpose for hail suppression.