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<br />S u r-fj-... <br /> <br />Reprlntedfrom Irrigation & Drainage <br />Session ProceedingslWaler Forum '92 <br />EE,HY,lR, WR DivlASCE <br />Baltimore, MDIAugusI 2-6, 1992 <br /> <br />TARGETING OF AgI IN A UTAH WINTER OROGRAPHIC STORM <br /> <br />by <br /> <br />James A. Heimbach, Jr.l and <br /> <br />Arlin B. Super <br /> <br />Abstract <br /> <br />A cooperative research program among the Utah Division of Water Resources, the <br />National Oceanic and Atmospheric Administration, and the Bureau of Reclamation has <br />investigated targeting of ground-released silver iodide during a winter orographic <br />storm. The cloud seeding material was transported at least 2 kIn vertically when <br />embedded convection was present. However, ice nuclei concentrations at ambient <br />cloud temperatures were likely too low for effective enhancement except in the <br />highest, coldest cloud turrets. <br /> <br />Introduction <br /> <br />An operational winter cloud seeding program has been conducted over several Utah <br />mountain ranges since 1973-74 (Griffith, et aI. 1991). Most silver iodide (AgI) <br />generators are operated in valleys west of the mountains and near canyon entrances. <br />Since 1981 a cooperative research program between the State of Utah and the National <br />Oceanic and Atmospheric Administration, and recently including the Bureau of <br />Reclamation, has been investigating the effectiveness of current seeding practices and <br />ways to improve them. A number ofresulting reports and publications have sugges.ted <br />problems with the transport and dispersion of the valley-released AgI during some <br />storm conditions. Super and Huggins (1992a, 1992b) refer to these earlierresu1ts, and <br />also present new findings from the 1989-90 field program. The overall evidence <br />suggests little silver (Ag) enhancement in the target areas' snowfall, and, during some <br />storm phases, frequent low-level trapping of the AgI or transport parallel to the <br /> <br />'Atmospheric Sciences. U. of North Carolina, Asheville, NC 28804-3299 <br /> <br />2Water Augmentation Group, Research and Laboratory Services Division,Bureau of Reclamation, <br />Denver, CO 8022~. <br /> <br />553 <br />