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Last modified
7/28/2009 2:38:42 PM
Creation date
4/16/2008 11:10:26 AM
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Template:
Weather Modification
Title
Final Report on Utah Cloud Seeding Experimentation Using Propane During the 2003/04 Winter
Date
3/1/2005
State
UT
Weather Modification - Doc Type
Report
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<br />I <br /> <br />I <br /> <br />I <br /> <br />common U.S. usage of inches of precipitation will largely be followed in this paper as they are more <br />meaningful to western water users. <br /> <br />I <br /> <br />Four gauges were located along the expected seeding plume trajectory, within the limitation of available <br />suitable gauge sites. These are shown on Figs. I and 2 as GSC, GRD, GTR and GDN. Gauge GSO was <br />located only 1.0 kIn south of the primary target gauge and was also treated as a target as discussed in Sec. <br />8. The other crosswind gauge, GNO, was 4.2 km north of the primary target gauge. It provided a suitable <br />control or covariate for the other gauges. The considerable care exercised to obtain accurate snowfall <br />measurements, and certain limitations of gauge siting, are discussed in detail in Sec. 5. <br /> <br />I <br /> <br />I <br /> <br />Wind speed and direction observations at the seeding site and primary target were used to estimate the <br />most likely periods of seeding plume passage by each target gauge, and by the instrumented targl~t station, <br />TAR, equipped with an ice particle monitoring probe. Periods of estimated plume passage were used in <br />calculation of the SWE amount which fell during each EU at each gauge. Those gauge observations were <br />the primary information used in statistical analyses. The seeding effect (or placebo) periods wen~ also <br />used for averaging measurements of ice particle concentration, winds, air temperatures, SL W pn~sence <br />and other parameters of interest at the TAR. The 40 min periods of propane release (or placebo) were <br />used for averaging observations immediately upwind of the HAS. These supporting observations were <br />used to partition gauge observations as part of the statistical analyses. <br /> <br />I <br /> <br />I <br /> <br />3b. Experimental Design of 2003/04 Utah Program <br /> <br />I <br /> <br />The primary purpose of the Utah 2003/04 winter seeding program was to conduct a randomized <br />experiment using propane seeding which could be tested by statistical methods. With the limited time <br />and funding available, it was decided that seeding had to be conducted at any hour of the day or night and <br />any day of the week, in other words, on a 24/7 basis. This approach offered the only realistic hope of <br />obtaining a sufficiently large EU population so that statistical testing might reveal a seeding effel:.:t at an <br />acceptable level of significance. EUs were kept brief, with propane releases of 40 min, because of known <br />rapid changes in cloud conditions. Longer periods would have been required to deal with plume passage <br />timing uncertainties had the downwind target dimension been significantly longer. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Earlier winter orographic randomized experiments have used much longer EUs, often the 24 h day. <br />But more recent microwave radiometer observations of SL Wand high resolution gauge measurements of <br />snow precipitation have demonstrated considerable short-term variability in winter orographic clouds, <br />indicating EUs much shorter than a day are more appropriate and better represented by supporting <br />observations used for partitioning. As shown in Table I of Sec. 7, correlation coefficients were relatively <br />high at 0.88 or 0.89 between the control and three of the target gauges for all available 40 min EUs. <br />Correlations calculated for daily totals for the same gauges had values between 0.89 and 0.98. fsee- <br />~ The large increase in sample size with briefer EUs more than compensates for the reduc:ed <br />target-control correlations. <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />The main temporal changes of concern were SL W presence and natural snowfall, shown to change <br />dramatically by numerous studies including Huggins (1995), Super and Holroyd (1997) and Holroyd and <br />Super (1998). EUs were obtained in pairs with a random decision made whether the first or last EU of <br />each pair would be seeded. The other unit in the pair was the untreated placebo used as a basis of <br />comparison with the seeded EUs. This pairing, or blocking, allows a particular type of statistical testing <br />common in some technical fields, but only recently suggested for weather modification experimlmts <br />(Gabriel 2000). This approach is discussed in detail in Sec. 7b. <br /> <br />I <br /> <br />To be reasonably confident that seeded ice crystals would usually be transported past a target, the HAS <br />high altitude seeding location and plateau top TAR and nearby precipitation gauge GTR, all successfully <br />used in prior experiments, were again activated. The horizontal distance between the HAS and TAR is <br />4.1 km although the actual seeding plume trajectory was likely somewhat greater, being largely I:.:ontrolled <br /> <br />I <br /> <br />6 <br /> <br />I <br />
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