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<br />that result in increases, no effect and decreases in precipitation when <br />seeded. They are used to help control variability in an experiment. They <br />are the basis for estimating the technical and economic feasibility of <br />seeding activities for an area. <br /> <br />The criteria for static seedability by the World Meteorological <br />Organization (WMO, 1982) also includes the requirement that the <br />coalescence process in the cloud be inefficient. This requirement is sup- <br />ported by Gagin (1981) who contends that clouds with an efficient <br />condensation-coalescence process are not colloidally stable, are capable of <br />generating precipitation particles quite efficiently and are~ therefore~ <br />less amenable to augmenting rainfall by static seeding. Moreover, since <br />the presence of an active coalescence process is associated with the likely <br />development of SICP, it is possible that SICP can generate ice crystals in <br />concentrations and at rates comparable to those intended by seeding. The <br />addition of more ice crystals by seeding in these situations is generally <br />regarded as contributing to "overseeding". <br /> <br />In considering the effects of SICP on static seedability, two types of <br />situations need to be considered; case 1: clouds in which the IRG mecha- <br />nism is dominant with an inefficient coalescence process, and case 2: <br />clouds in which the CRG mechanism is dominant with an efficient coalescence <br />process. In case 1, it has been commonly assumed (but not proven) that <br />SICP occurs mainly by the rime-splintering process. Gagin (1981) argues <br />that the occurrence of SICP in such cases is not a deterrent to static <br />seeding. He claims that the initial ice concentrations in the cloud deter- <br />mines the graupel concentrations that will develop (Gagin, 1975) and, since <br /> <br />9 <br />