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Show periodicity in the treatment is destroyed; e. g. Daisy 39 - no periodicity, and material found within 1 mile or less of the release point one hour after release terminated, even though near-release-point wind was 3. 7 mph. As regards modeling diffusion in the Park Range, under neutral stratification through a deep layer above the release point with a simple wind profiler the standard diffusion model, i. e. Pasquill-Gifford, is adequate for predicting the distribution of _nuclei. Under stable conditions the direction of the whole plume is often controlled by the flow in a very thin layer (500 ft. ) and the modeling of the vertical and horizontal distributions is at best extremely diff. icult. No single existing model is applicable to dispersion conditions under stable stratifications in mountainous terrain. 3. 2. 2 Airborne Releases Airborne seeding is, for most conditions, an inherently more reliable treatment system because of the complex dispersion and transport variations near the surface in mountainous terrain. The best way to uniformly treat a large volume utilizing an aircraft delivery system has yet to be determined however. The present pyrotechnic devices consist of a flare attached to an aircraft, or a falling flare dropped from an aircraft. The spread of these initially nearly zero area vertical or horizontal line sources is of extreme importance in defining the treatment of a volume. An important question is how far upwind of the actual target area a release must be made to avoid initial overseeding of a part of the target volume. The magnitude of ~he effects produced by overseeding an initial volume has not been determined, but experience indicates that it is wise to avoid overseeding in any initial precipitation-producing_ volume. In conjunction with the aircraft seeding program conducted in the Park Range during the 1968-69 winter season, a series of diffusion tests was conducted to answer some of these questions. Two aircraft were used in these tests, a Cessna 180 with aerial seeding capability and a Queen Air with nuclei trackin~ capability. For some tests a second tracer system was also used. Lithium stearate was released from the seeding aircraft and atmospheric lithium con· tent was monitored on the ground at the Rabbit Ears Pass site with a flame photometer (Hogan and Rich, 1968). 3. 2. 2. 1 Results On 12 March 1969, a single line source was released on a north-south line just west of Mt. Harris at 11, 000 ft. MSL. The pyrotechnic used was an Olin No. 1006 flare which released approximately 2 x 1014 nuclei per kilometer of flight track. The release was centered at 1230 MST; Figure 48 indicates the trace from a sampling track at 1247 MST. After 17 minutes and 10 kilometeri of travel, note that the plume had spread to 4. 3 kilometers width and the peak 82 |