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<br />0027J3 <br /> <br />that there was no significant statistical difference between seed and no-seed <br /> <br /> <br />events for the project for the 24-hour experimental day evaluation, but there <br /> <br /> <br />were specific instances of positive and negative effects for shorter three <br /> <br /> <br />and six-hour periods. <br /> <br /> <br />We need to find what the meteorological and topographical conditions were <br /> <br /> <br />that led to the positive and negative effects. <br /> <br /> <br />The seven projects studied in the generalized seedability analysis were: <br /> <br /> <br />the Bridger Range in Montana; Climax in Colorado; the Colorado River Basin <br /> <br /> <br />Pilot Project; Jemez in New Mexico; Pyramid Lake Pilot Project in Nevada; <br /> <br /> <br />Censare in California; and the Santa Barbara Project in Southern California. <br /> <br /> <br />We looked at a total of 1,248 (six-hour) cases with reference to four major <br /> <br /> <br />meteorological categories. The four categories were stability, snow trajec- <br /> <br /> <br />tories, cloud moisture, and cloud-top temperature. A description of the pa- <br /> <br /> <br />ameters in each project and the four categories are described in Vardiman and <br /> <br />Moore (1976), <br /> <br /> <br />The first set of parameters, shown in Figure 1, were: a smooth stable <br /> <br /> <br />cloud with the snow calculated to fall on the crest, moderate cloud moisture, <br /> <br />and cloud-top temperature between -lOoC and -30oC. Of the 1,248 cases, 211 <br /> <br /> <br />had this set of conditions. In these 211 cases, there was a seed/no-seed <br /> <br /> <br />ratio of 1.405 or a 40% increase in precipitation due to cloud seeding. This <br /> <br /> <br />was true using a Hilcoxin statistic at the .001 level (one chance in a thou- <br /> <br /> <br />sand that there was no difference between seed and no-seed precipitation). <br /> <br /> <br />The second set, shown in Figure 2, of which there were 121 out of 1,248 <br /> <br /> <br />cases, had the same parameters with the exception that rather than a stable <br /> <br /> <br />cloud these clouds had moderate instability (i.e. there was slight convection). <br /> <br /> <br />In these cases, there was a 130% increase in precipitation indicated with a <br /> <br /> <br />probability of .002. If the probability is less than ,05, we are in good shape. <br /> <br /> <br />The third set of cases, shown in Figure 3, involved the same set of con- <br /> <br />ditions except for high instability in the cloud (convection building quite <br /> <br /> <br />rapidly), There were 150 cases in this set with a 48% increase in precipita- <br /> <br />tion at a probability of .007. These three groups of cases accounted for 486 <br /> <br /> <br />of the 1,248 cases and overall they showed a 52% increase in precipitation at <br /> <br />less than ,001 probability, <br /> <br /> <br />Now for negative effects, Hith a stable cloud, moderate to high water <br /> <br /> <br />content, -lOoC to -30oC cloud top temperature, and a blow-over trajectory, the <br /> <br />I <br /> <br />j <br /> <br />4 <br />