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<br />about the mid-1960's, before the importance of the CRG mechanism was first <br />established, the implied strategy had to be the improvement of the effi- <br />ciency of the IRG mechanism. In experiments conducted after that date the <br />implied strategy is less clear, but their references to the Bergeron pro- <br />cess indicates that the physical hypothesis continued to be based on the <br />IRG mechanism. In fact no cause-and-effect argument has been presented <br />which details how the efficiency of the eRG mechanism can be improved by <br />glaciogenic seeding. <br /> <br />3. Seedability <br /> <br />According to the static seeding hypothesis a cloud is postulated to be <br />seedable (WMO, 1982) if it contains supercooled water that is or will be <br />under-utilized by the cloud's natural precipitation process, that will not <br />be eroded by competitive depletion processes and that will last long enough <br />in sufficient quantities to permit the growth of additional precipitation <br />particles induced by seeding to sizes that can reach the ground. If the <br />amount and persistence of supercooled water in a cloud is high, then the <br />depletion rate of water associated with natural precipitation development, <br />cloud ice evolution and entrainment is likely to be low, and the oppor- <br />tunity for seeding tends to be high. The coexistence of ice in the cloud <br />is only a deterrent to seeding if it exists in sizes and concentrations <br />which causes the supercooled water to be depleted faster than seeding can <br />exploit it. <br /> <br />Seedability criteria are a practical expression of the physical hypothesis. <br />They are used in an attempt to distinguish and select among those clouds <br /> <br />8 <br />