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OOZ:>J3 suggested that the best opportunities for seeding are days with 500-mbar temperatures above -8 'c and a 400- to 700-mbar wi nd shear less than 11.83 mis, with the updraft peaking in the upper third of the cloud. Cloud seeding material and methods of dispersion were compared between the South Dakota Rapid Project (using silver iodide from ground-based generators, dry ice, and silver iodide/ammonium iodide/acetone solutions from airborne generators, and some pyro- technic devices) and the North Dakota Pilot Project (using only silver iodide/ammonium iodide/acetone solutions). Findings indi- cated that cloud selection is more important to the results than the exact seeding treatment. CONTRACTOR: Illinois State Water Survey, Urbana, Illinois CONTRACT NO. 14-06-0-7197 PRINCIPAL INVESTIGATOR: Stanley A. Changnon, Jr. PERIOD: July 1, 1974, to November 30, 1977 FUNDING: FY75 - $ 54,200 FY76 - $136,271 T.Q. - $ 48,317 FY77 - $195,749 FY78 - $ 1,983 I r ~ f ~ This multiyear contract was initiated in 1971. The first 3-1/2 years were devoted to a series of 10 background studies for the design of a precipitation modification experiment in Illinois. A reduction in funding ended that program prematurely. Results of those studies are reported in the Skywater 1973-74 Biennial Report.2/ Essentially, the social and environmental impact studies indicated the desirabil- ity of precipitation management. Activities in the last 2-1/2 years of the contract focused on prepar- ation of the HIPLEX design document, "Design of the High Plains Experiment with Specific Focus on Phase 2, Single Cloud Experimenta- tion." The design calls for (1) exploratory studies to provide basic data for developing specific modification hypotheses and monitoring systems, (2) a single cloud rain modification experiment to establish scientific certainty of the consequences of seeding relatively simple, semi-isolated clouds, and (3) an area rain modification experiment to develop an overall level of confidence in producing a net benefit from seeding both simple and more complex cloud systems over large areas of the High Plains. I The design report suggests in general terms the modification hypoth- eses for the single cloud seeding experiment (static and dynamic seeding), the statistical design and evaluation procedures appropri- ate for a single cloud experiment, and the operation aspects of a 2/ See footnote 1 in this section. II 1-6