Modeling the Microphysical and Dynamical Effects of Silver Iodide Seeding of Warm-Based Convective Clouds

A three-dimensional convective cloud model was used to simulate the impact of silver iodide(AgI) seeding on a subtropical convective storm that occurred on 8 July 2004 in Anhui Province, eastern China.The primary goal was to further understand the microphysical mechanisms of precipitation formation in warm-based convective clouds, and to investigate the microphysical and dynamical effects of AgI seeding.The characteristic structure of the observed storm was reproduced well by the simulation.Autoconversion of cloud water to rain and melting of graupel were the major sources of raindrops, contributing 67%(19%) and 18%(57%) of total raindrop number(mass) concentration, respectively. AgI seeding carried out in the early stages of clouds in the main updraft regions resulted in substantial increases in rain and decreases in hail.The seeding increased graupel mass and thereby inhibited hail formation in the early stages, but enhanced rain formation and growth.The seeding also enhanced secondary convection and caused the cloud to process more water vapor and thereby cloud water, leading to increases in both the autoconversion of cloud water to rain water and accretional growth of cloud water by rain and hail and, ultimately, rain and hail enhancement in the later stages. Furthermore, seeding resulted in a redistribution of precipitation on the ground.These results indicate that AgI seeding could significantly influence the cloud microphysics, dynamics and, subsequently, the precipitation of warm-based convective clouds.