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<br />~ <br /> <br />were of basically two forms: (1) detailed case studies using all available <br />data types, and (2) statistical analysis of precipitation data under various <br />data stratifications. <br /> <br />1. 5 Summary of Conclusions <br /> <br />The detailed case study analyses of H)68-69 data yielded strong evidcnc'(' of <br />positive seeding effects in several individual cases, and unequivocally proved <br />that (1) silver-in-precipitation concentration was notably higher in seedc'd, <br />as compared to unseeded periods, (2) silver iodide particles did, in fad, <br />serve as active ice nuclei, and (;3) seeded snow crystals were prcdominC1,ntly <br />- --.- --~.._,.... <br />small hexagonal plates. <br /> <br />--::.:~_._...~._-- ,-. '~""'."-'<~~-' <br /> <br />The statistical analysis of 1968-69 <lata consisted of a non-parametric sum <br />of squared ranks test (Mielke, 1967), applied to each individual station's <br />optical snow sensor record after a series of stratifying routines had been <br />imposed. Results showed statistically significant precipitation increases at <br />Rabbit Ears Pass for cloud top temperatures .: - 200C, and decreases fOT <br />colder conditions. This result is in agreement with reported work of Grant, <br />ct. at (1968). <br /> <br />II! <br /> <br />The study demonstrated the usefulness of several supporting measurements <br />and techniques. In particular, the methods for det.ecting silver in snow and <br />silver iodide nuclei in snow crystals were invaluable in interpret.ation of <br />experimental results. The diffusion tests and numerical modeling of oro- <br />graphic flow and precipitation both led to increased understanding of seeding <br />requirements for orographic precipitation. It has been concluded that an <br />operational seeding program should include both ground and airborne delivery <br />systems. Criteria for seeding and choice of seeding technique were developed <br />on the basis of the combined experimental results. <br /> <br />It has been concluded that precipitation increases of 100% or greater'- could <br />be achieved for the Park Range, when cloud top temperatures are warmer <br />than -20oC, by using a combination of ground and airborne seeding. Given <br />perfect predictions of cloud top temperature, detrimental seeding effects <br />produced when cloud temperature is less than -240C could be eliminated. <br />For reasonably attainable c loud temperature prediction capability, it is esti- <br />mated that a $.~asQnaL cumJ.llati.ve~~eding effect of 25% increase in ~precipi.":'-- <br />.--'" .. ,. " .----.--, <br />t~tion cOUl(LQ~echieved il~ practi~~.:. <br /> <br />1. 6 Report Outline <br /> <br />Section 2. 0 of this report describes the field operations', equipment, and <br />techniques that were used in the Park Range experiments. Instrumentation <br />and methods developed specifically for this program are presented in detail. <br />Section 3. 0 describes, and summarizes the results of, supporting studies, <br /> <br />, <br /> <br />5 <br /> <br />-~~-- <br />