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CONTRACTOR: South Dakota School of Mines and Technology, Rapid City, South Dakota CONTRACT NO. 5-07-DR-12100 PRINCIPAL INVESTIGATOR: Harold Orville CONTRACT PERIOD: July 1, 1975, to January 31, 1979 FY79 FUNDING: None PURPOSE: Development and application of a two-dimensional, time-dependent convective model A two-dimensional, time-dependent cloud model is being used to simulate microphysical and dynamic processes in convective cloud systems and to identify the effects of silver iodide seeding. Results indicate that the potential to augment precipitation is closely related to dispersion of the correct amount of seeding agent into the proper region of the cloud at the appropriate time to obtain optimum effects. Information developed to predict dynamic interactions between clouds as a result of seeding is especially important as HIPLEX progresses toward an exploratory experiment. The model, originally developed for mountain clouds, was modified to realis- tically simulate convective clouds of the High Plains region. An important finding in the cloud simulation is that very strong downdrafts and outflows are caused by an evaporating rainshower. The associated high-velocity horizontal winds may cause aircraft to stall when landing. Similar condi- tions appear every summer in the High Plains. Three case studies from Montana and Texas have been analyzed and compared with actual observations. Results indicate a "time window" for the icing process in natural (unseeded) cases. This window is related to the concen- tration of natural ice nuclei and windflow patterns. Ice precipitation processes were shown to be dominant in Montana. Model simulations include dry ice and silver iodide seeding techniques. Two methods of simulation include direct creation of precipitating ice at the expense of supercooled cloud water and the evolution of ice through disper- sion of seeding agent throughout the cloud by internal dynamics. The latter method produces more precipitation than the former if the cloud is seeded early enough in its life cycle in the major updraft region. Studies show that mesoscale environmental lifting also is an important control of convective instability and moisture. Hypothesis development and numerical analysis of response variables are continui~g in support of the HIPLEX design and evaluation plan. CONTRACTOR: Environmental Research and Technology, Inc., Concord, Massachusetts - CONTRACT NO. 14-06-D-7673 PRINCIPAL INVESTIGATORS: Kenneth Hardy and C. A. Grainger CONTRACT PERIOD: April 15, 1975, to July 31, 1980 FY79 FUNDING: $268,338 PURPOSE: Conducting and supporting weather modification research in Kansas 1 "