Numerical Simulation of the Influence of Drop Size Distribution Shape on Cloud and Precipitation

At present, parameterization methods to describe cloud and precipitation processes are widely used in cloud and mesoscale models, but with different drop size distributions. When precipitation formation mechanism, weather modification technique, and mechanism of hail suppression with seeding are studied by using these models, a question that needs to be addressed is: what is the influence of different drop size distributions and related parameters on cloud and precipitation? In this paper, by using a three-dimensional hail cloud numerical model developed by the Institutes of Atmospheric Physics, Chinese Academy of Sciences,we performed numerical experiments with varied drop size distribution parameters for two hail storms, and analyzed the influence of shape parameters (ar, ai, and ag) of raindrops, ice crystal, and graupel size distributions on rainfall, hail amount, and microphysical processes in clouds. The results show that the variation of ar has no effect on precipitation formation on the whole, but affects directly the production rates for the physical processes related to raindrop. The ag variation has a less obvious effect on rainfall amount, but has a significant effect on hail amount, hailfall rate, and rainfall intensity. It impacts noticeably on the generation rate of the number and mass of ice crystal, graupel, and hail, and also to various degrees on all the microphysical processes in clouds. The ag variation also influences the growing process of the hydrometeors. The effects of the ai variation on part of the generation and growing processes of all the hydrometeors are significant, and even dramatic, such as the collection process of cloud water to rain through melting ice crystal (TCLcir). However, for clouds located in different geographic regions, the variation of ai has different effects on precipitation, which reflects the complexity of the impact of drop size distribution on cloud and precipitation. At last, some issues about the application of cloud models are also discussed.