The Numerical Simulation of Weather Modification By Cloud Seeding

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9630008 Orville This research continues ongoing investigations into the numerical simulation of cloud seeding effects on the cloud scale and mesoscale. The work is broad based, treating stratiform orographic clouds and hailstorms over the northern High Plains. Models have been developed at the South Dakota School of Mines and Technology (SDSM&T) that simulate the development of clouds, rain, snow, and hail. Methods have been developed that treat the numerical simulation of the seeding of convective and stratiform clouds. The simulation of the seeding agent involves the release of the agent, the spread of the seeding agent throughout the atmosphere, and the interaction of the seeding agent with the supercooled liquid water in the cloud. Only in the past few years have these methods been incorporated into fully three- dimensional, time-dependent models. This allows, for the first time, the many hypotheses of the cloud seeding community to be tested in the strongest scientific frameworks, although many useful insights and greater understanding have resulted from lesser dynamic frameworks. Studies of winter/spring situations will be carried out. In addition, the pattern of summer convection, as detected by radar pattern climatology leads to much different precipitation patterns than in the winter. The Principal Investigators also will simulate those patterns. These summertime cloud situations will allow testing of the effects of simulated seeding on the merging of cloud cells, an important effect detected in field experiments in previous research. The seeding of hailstorms has been simulated and is revealing intriguing results. Whether or not the storms have an active coalescence process and the lifetime of the cells determine the degree of response to the seeding. Also, the timing and the placement of the seeding material are important for the seeding to be effective. Further work is needed to strengthen the theoretical basis. The m odel being used for this work simulates the formation and development of the precipitating ice particle spectra. Such detail is necessary if conclusions are to be drawn concerning the effects of cloud seeding on hailstorms. The Principal Investigators also have developed models that simulate the processes of atmospheric electricity in clouds. The numerical simulations of seeding effects on the storm s microphysics will be applied to a vigorous thunderstorm and analyzed as to their effects on the storm electrification. Successful completion of this research should lead to increases in understanding of the microphysical processes involved in precipitation production and storm electrification.