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<br />3.9.3 Randomization <br /> <br />Morning seeding of the west target pair and afternoon seeding of the east target pair will <br />each be separately controlled by their own sequential lists (envelopes) of experimental unit <br />decisions to seed or not seed the northern target area of the pair (if not treated is drawn, the <br />southern target area of the pair is treated). Block randomization will be used in each case <br />to ensure that each target area in the pair is treated about the same number of times. <br /> <br />3.9.4 Type of nucleant and means of delilvery <br /> <br />The nucleant to be used in this experiment will be the exothermic hygroscopic chemical <br />CaCI2. The CaCl2 is acquired from the manufacturer in relatively small-size particles and <br />packaged in 25-kilogram bags. During seeding operations, the bags are slit open just prior <br />to seeding and the contents are poured into a hopper that empties into the airstream below <br />the fuselage of the aircraft. <br /> <br />The aircraft speed during seeding is about 120 knots. The seeding chemicals are dispensed <br />(poured out) from the aircraft at a rate of about 75 kilograms per minute. Thus, the average <br />seeding dosage is about 21 kilograms per kilometer. <br /> <br />The size distribution of the CaCl2 at the time of milling by the manufacturer is generally <br />known; however, this size distribution shifts to larger sizes as a result of clumping during <br />storage and handling in the high humidity environment of Thailand. Because CaCl2 absorbs <br />moisture at very low relative humidity (about 18 percent), great care must be exercised <br />during the storage and handling process to maintain the original size distribution of the <br />particles. Given the relationship of the size distribution of the hygroscopic chemicals to its <br />payload effectiveness (appendix D), it is important to prevent the degradation of size <br />distribution of the hygroscopic chemicals that will be used in the seeding operation. <br /> <br />3.10 Experimental Procedures <br /> <br />The experimental procedures that will be used in the warm cloud demonstration project are <br />discussed in detail in "Volume 3 - Demonstration Project Operations Plan." The two-area or <br />target-control design involves a random choicl:! of either treating or not treating experimental <br />units associated with a specified target area; however, measurements are also obtained from <br />a control area. The analysis of results is based on differences between target area <br />measurements for treated and nontrea.ted experimental units; however, observations in the <br />target area are adjusted on the basis of observations in the control area, thereby accounting <br />for some of the natural variability. <br /> <br />The experimental unit is terminated if more than 60 minutes have elapsed since the end of <br />treatment. The experimental unit can also be terminated by failure of the measurement <br />and/or seeder aircraft and/or the monitoring S-band radar. In addition, the experimental unit <br />can be terminated if the seeding required by the randomization decision cannot, for any <br />reason, be carried out as prescribed by 1Ghe conceptual model. These operational failures shall <br />serve as the basis to discard the unit. <br /> <br />29 <br />