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<br />I <br /> <br />p <br /> <br />Seeding Agents and Dispensing Rates <br /> <br />The active agents used for the reported weather modification activities <br />were silver iodide (AgI), crushed frozen carbon dioxide (dry ice (C02)), <br />polye1ectro1ytes, propane, charged water droplets, urea, compressed air, <br />and lead iodide. Table 5 shows clearly that AgI was used in most of the <br />reported activities, both air and ground-based. Dry ice followed far be- <br />hind as the second most used agent in the 3 years. In many projects, two <br />or three modification agents were used. <br /> <br />Dispensing rates for the seeding materials varied with the location of <br />the apparatus, the type of equipment, llild the purpose of the activity. <br />For example, the dispensing rate for AgI from one ground-based, arc-type <br />generator used for increasing precipitation can be set at 0.5 or 2.0 grams per <br />hour. A single, ground-based, propane fired liquid-fueled generator can <br />dispense up to 22 grams of AgI per hour. One liquid-fueled generator on an air- <br />plane can dispense 240 grams of AgI per hour. A single pyrotechnic flare <br />attached to the aircraft wing will burn for about 5 minutes with an output <br />of 75 grams of AgI; an ejectable flare ",ill burn for about 30 seconds and <br />emit 5 to 20 grams of AgI. When dry ice is used, the dispensing rate is <br />measured in kilograms per hour from the airplane during its traverse of <br />fog or clouds. <br /> <br />Summary of Reported Data <br /> <br />Table 6 presents a sunnnary of data submittl~d for activities in calendar <br />years 1976, 1977, and 1978. These data show the small amount of Federal <br />experimental and operational weather modification carried out in the United <br />States. Federal operational activity was confined to cold fog dispersal at <br />Air Force bases in Alaska and Washington. Also apparent is the limited <br />number of days devoted to weather modification research. As in past years, <br />the hours of operating ground-based AgI generators are much greater than <br />the hours of aircraft seeding. However~ high aircraft seeding rates allow <br />larger quantities of AgI to be dispensed in a shorter time. <br /> <br />The amount of dry ice used in CY 1978 was about 38 percent less than the <br />2 prior years. This reduction was due to fewer cold fog modification days; <br />the activity reports reveal that more projects are using dry ice for pre- <br />cipitation enhancement than in earlier years. The use of polyelectrolyte <br />was drastically reduced over the 3 years. <br /> <br />11 <br /> <br />1-..... ._1 <br />