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<br />either among clouds in the target area or between the target and downwind <br />areas. This implies that either a) all clouds are seedable, b) clouds that <br />are not seedable will not effect precipitation adversely, or c) if negative <br />effects do occur, they are outweighed by the positive effects. The results <br />of the Israeli experiments (Gagin and Neumann, 1981) seem to indicate that <br />condition (b) prevailed. However, the results of Project Whitetop (Flueck, <br />1971) and the Arizona Project (Battan, 1966; Battan and Kassander, 1967) <br />seem to represent situations where none of these conditions are met; <br />rather, the non-selective seeding was counterproductive. The inability to <br />predict and isolate the occurrence of seedable clouds (see section 3) <br />further compound the above-mentioned engineering problems in ground-based <br />seeding that must be overcome. <br /> <br />5. Chain of physical events <br /> <br />HIPLEX-1 (Bureau of Reclamation, 1979) was a randomized, double-blind <br />experiment to test the static mode seeding concept for convective clouds. <br />It specified in advance and attempted to verify by observations during the <br />course of the experiment each step leading to additional precipitation at <br />cloud from base from seeding. It was similar in approach to experiments <br />conducted by Braham et al. (1957) and Bethwaite et al. (1966) but more of <br />the steps in the chain of physical events could be included because of <br />recent developments in observing, measuring and real-time data processing <br />capabilities. Therefore, the HIPLEX-1 design (Bureau of Reclamation, 1979; <br />Smith et al., 1984) and physical results (Cooper and Lawson, 1984) will be <br />used as the framework for the discussions to follow. They will also serve <br />to illustrate the concepts discussed in the foregoing sections. <br /> <br />26 <br />