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<br /> <br />go parallel to the barrier. Temperature inversions or stable <br />layers near the surface accentuate this effect and may cause ice <br />nuclei from ground generators to be trapped and thus not seed <br />the clouds at all. Another possibility is that artificial nuclei <br />may continue to enter the clouds after it is desirable if disper- <br />sion has been retarded. Perhaps the best delivery technique for <br />the treatment of seeding opportunities is a combination of ground- <br />based and airborne systems, depending upon atmospheric conditions. <br />Uncertainties related to the targeting of the cloud seeding <br />material that were stated above demonstrate the need to conduct <br />diffusion and tracer studies in conjunction with cloud seeding <br />operations. These studies would be directed toward identifying <br />the meteorological conditions for which seeding with ground-based <br />artificial ice nucleus generators is the most effective and 1:hose <br />which are not effective. A related question that needs to be <br />addressed is at what elevations on the mountain barrier can <br />tracer material be identified? The target for winter orographic <br />cloud seeding is the mountainous area generally located at <br />elevations above 9,000 feet MSL. The local populace desires the <br />documentation that there is no seeding effect below 8,000 feet <br />MSL upwind of the target area. They also desire to know to ~mat <br />extent the region between 8,000 and 9,000 feet MSL is affected. <br />Observations need to be made that will provide this assurance and <br />information. <br />The ecological and sociological interactions of cloud <br />seeding progranls definitely need to be considered. These con- <br />siderations cannot be an afterthought; they have to be part of <br />the planning process for any precipitation augmentation project. <br />Studies which have been conducted, specifically the San Juan <br />Ecology project~,9 have led to a consensus in the scientific <br />community that no significant environmental effects will occur <br />during the time frame spanned by a five-to-ten-year cloud seeding <br />program. However, some environmental monitoring should accompany <br />long-term opera.tional programs to act as a barometer for any <br />subtle environrr~ntal changes that could indicate future significant <br />effects upon the ecology of the area. <br /> <br />-14- <br /> <br />K~ <br /> <br /> <br />~ <br />