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<br />5.2 Prior Results from Colorado Sampling <br /> <br />Some limited experimentation using instrumented aircraft and an acoustical ice nucleus <br />detector was reported by Reid (1979). This was done in conjunction with a weather modification <br />experiment near Climax, Colorado. An i\gI generator was operated south of RedditT, Colorado, <br />near the location of AgI generator 17 on Figure 1, during periods with northwest flow aloft. <br />Supporting information was obtained from wind instruments in the valley over two winters. <br />These observations revealed that about half of the hours on precipitation days had downslope <br />drainage flow implying a stable environment with flow near generator levels opposite to winds <br />aloft; that is, away from the intended target. The aircraft measurements indicated great <br />complexity in T &D in mountain valleys including a high frequency of shallow flows, both up <br />and down valley, and strong terrain channeling. A high frequency of capping inversions was <br />found that essentially trapped the AgI for extended periods. In brief, seeding with a valley <br />generator to affect the atmosphere thousands of feet higher in a desired "downwind" but upslope <br />direction was found to be impractical much of the time. <br /> <br />Rangno and Hobbs (1993) presented particle trajectory analyses for the Climax I and 11 <br />experiments southwest flow category. That category had the greatest seeding effect indicated from <br />statistical analyses. They calculated that only the Leadville AgI generator (between Agl generators <br />13 and 14 on Figure 1) could have targeted Climax for (interpolated) 700 mb winds (near 10,000 ft) <br />from the southwest. The generator to target distance was over 12 miles and ridges between them <br />rose over 2,500 ft above the generator. Back-trajectory analyses for ice particles that actually fell at <br />Climax showed the particles had to have originated far above the generator elevation. Inspection of <br />surface winds near the generator showed little correlation between them and 700 mb winds. For <br />many experimental days with southwest flow at 700 mb, winds at the generator were not toward the <br />Climax target. They authors concluded that, "Winds at a key generator site often blew away from <br />the target on those days for which maximum seeding effect have been claimed." Their analyses <br />present further evidence of the complications involved in attempting to use surface AgI generators, <br />even when located in high mountain valleys, to target higher rugged terrain. <br /> <br />Several past studies of the T &D of ground-released AgI or tracer gas were reviewed by <br />Super (1999b), also published as Appendix A of Medina (2000). Investigations dealing specifically <br />with Colorado are reproduced in the following three paragraphs: <br /> <br />"Some of the earliest airborne AgI plume tracking results over the Headwaters Region were <br />reported by Langer et al. (1967) during testing of a new ice nucleus counter. A limited data set <br />resulted, 'under conditions approximating those conducive to cloud seeding.' It was found that <br />much of the AgI released from the 8,200 ft top of Emerald Mountain was trapped in the Yampa <br />valley between the release point and the Park Range. None of the tests showed reasonable AgI <br />concentrations more than a few thousand feet above the ground. <br /> <br />Smith and Heffernan (1967) commented that the Langer et al. (1967) results were in <br />agreement with their more comprehensive series of measurements of AgI plumes released from an <br />Australian mountain top. They stated that under their conditions AgI should be released from <br /> <br />24 <br /> <br /> <br />