Studies on Microphysical Processes in Hail Cloud
Hong Yanchao, Xiao Hui, Li Hongyu and Hu Zhaoxia(Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijng 100029)
Abstract Microphycical processes in hail cloud are studied by simulations of a 3-D hail cloud numerical model. The results indicate that each kind of ice particles has its generation /one and growth zone in the cloud. In a developing stage of the hail cloud maximum production rales of graupel, fro/en drop, hail stone and rainwater are all situated in the vicinity of 6 km height, the hail embryo and hail generation zone. From the "benefit competition" concept, the optimum seeding position for hail mitigation should be located there. Processes of the particle generation and growth in the different developing stages of cloud are different. In hail formation, growth of graupel and frozen drop as hail embryo is mainly by the accretion processes. The growth amount by the accretion occupies the most part of the to tal growth amount. Plenty of supercooled rainwater is very important in the formation and growth of hail embryos and hailstones. In the chain of " ice crystal-hail embryo-hailstone" , if there is not supercooled water, strong hailstone shooting would not occur. A contrast study of two observational hail clouds shows that when the temperature declines and humidity raise at the cloud base, the quantity of graupel embryo increases greatly because the amount by the accreting to suppercooled water, especially cloud water, is increased by a wide margin, the size of graupel is increased, and the conversion rate of graupel to hail is raised.