Results from the 1989 Exploratory Cloud Seeding Experiment in Illinois by

An exploratory cloud seeding experiment designed to modify clouds to augment rainfall was conducted in Illinois during the summer of 1989. This field experiment was carried out as part of the Precipitation Augmentation for Crops Experiment (PACE) initiated by the Illinois State Water Survey in 1978 with support from the National Oceanic and Atmospheric Administration. Findings after adjusting for sample bias indicate visual evidence for seeding effects on cloud tops; no evidence of enhancement in echo size or growth from seeding; and a weak suggestion of a possible rain increase in cloud groups that had been treated with silver iodide. This report also considers the implications that the results pose for the design and direction of future weather modification research, as well as for the practical use of cloud seeding in Illinois. Reference: Czys, R.R., S.A. Changnon, K.R. Gabriel, M.S. Petersen, R.W. Scott, and N.E. Westcott, Results from the 1989 Exploratory Cloud Seeding Experiment in Illinois, Illinois State Water Survey, Champaign, Bulletin 72. Indexing Terms: Cloud seeding, weather modification, precipitation enhancement, dynamic seeding hypothesis, cloud physics, radar meteorology, forecasting, predictor variables, response variables, sample bias, radar-estimated rainfall. STATE OF ILLINOIS HON. JIM EDGAR, Governor DEPARTMENT OF ENERGY AND NATURAL RESOURCES John S. Moore, B.S., Director BOARD OF NATURAL RESOURCES AND CONSERVATION John S. Moore, B.S., Chair Robert H. Benton, B.S.C.E., Engineering Donna M. Jurdy, Ph.D., Geology H.S. Gutowsky, Ph.D., Chemistry Roy L Taylor, Ph.D., Plant Biology Robert l_ Metcalf, Ph.D., Biology W.R. (Reg) Gomes, Ph.D. University of Illinois John H. Yopp, Ph.D. Southern Illinois University STATE WATER SURVEY DIVISION Mark E. Peden, Acting Chief 2204 GRIFFITH DRIVE CHAMPAIGN, ILLINOIS 61820-7495

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