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<br />the rime-splintering process occurs only after graupel is present, some <br />10-20 min after ice crystals first appear, there is time to influence the <br />precipitation efficiency of the cloud through static seeding. In case 2, <br />SICP can occur by both the rime-s~intering and freezing-splintering mecha- <br />nisms and sufficient time may not be available to influence the precipita- <br />tion efficiency of the cloud. When the coalescence-grown drops freeze to <br />form graupel embryos, SICP by the freezing-splintering process occur's right <br />away. In addition, since the graupel embryos that develop in this ~/ay are <br />initially rather large, time is fairly short before the rime-splintering <br />process becomes active. Therefore, ice phase seeding of such clouds. may <br />contribute to "overseeding". <br /> <br />It is interesting to note that those experiments which resulted in sta- <br />tistically significant decreases or redistribution of precipitation <br />involved clouds in which the CRG mechanism was probably dominant: Koenig <br />(1963) and Braham (1964) documented its existence in Whitetop (Flueck, <br />1971); Battan (1963) inferred from the height of first radar echoes in <br />Arizona that the coalescence process was the dominant precipitation ini- <br />tiation mechanism in convective clouds that grew well above the freezing <br />level, from which it can reasonably be assumed that the CRG mechanism was <br />operative during the Arizona Project (Battan, 1966; Battan and Kassander~ <br />1967); and the occurrence of the CRG mechanism in Necaxa (Perez-Siliceo, <br />1970) clouds is assumed to be likely based on reasoning related to cloud <br />base temperature that was discussed above. In fact, the negative results <br />of Whitetop have been attributed to "overseeding" (Braham, 1979). The <br />results of the model seeding experiments by Nelson (1979) also support this <br /> <br />10 <br />