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Show 1. 2. 2 Randomiz ed Seeding Design A compl ete change in operational routine was made for the 1968-69 season, w ith randomi zed seeding for only one hour of a six-hour intensive data collec tion block. Seeding modes included ground generators at Mt. Harris, and aircraft seeding , using droppable pyrotechnics or wing flares. Under this seeding design, the seeding releases were sufficiently short in duration relative to the unseeded periods to allow the collection of both seeded and truly unseeded data. Thus, significant results were obtained using this d es ign. 1. 3 Development and Use of Special Equipment and Observing T echniques It was recognized at the outset that if the project objective were to b e accomplished in the short span of allotted time, high resolution measurements of precipitation rates and vertical profiles of wind, temperature, humidity and stability would be required. Also helpful in isolating seeding effects would be supporting physical measurements such as ice nucleus counts, silver-inprecipitation, and the presence .(or absence) of silver iodide particles acting as snow crystal nuclei. Therefore, a number of special techniques were developed or adapted for use in the experiments. 1. 3. 1 Precipitation Rate Measurements An optical snow-rate sensor with 2 minute time resolution, capable of operating r ·emotely for a week, was developed and used extensively throughout the project in a dense data collection network. Modified weighing bucket gauges, special Soil Conservation Service snow course water equivalent measurements, and snow pillows were also used as backup data (but with less time resolution). 1. 3. 2 Ice Nucleus Measurements and Inert Tracers Surface measurements of free air ice nucleus count were made continuously during operational periods at Rabbit Ears Pass, and frequently at additional locations, using an NCAR-Bollay acoustical ice nucleus counter. Phosphorescent zinc cadmium sulfide was frequently released as a dual tracer simultaneously with Agl releases during the 1965-66 season, and collected snow samples were melted and analyzed for phosphorescence with the aid of a sensitive photo-multiplier device. On a few occasions during the past three seasons, lithium stearate was released as an inert tracer. Air samples were sensed at Rabbit Ears Pass for lithium with a flame photometer, in a cooperative program with the State University of New York at Albany. 1. 3. 3 Snow Sample Collection and Analysis During the course of the project two thousand snow samples were collected on 3 ft. x 3 ft. plastic sheets at 5 to 30 minute intervals. These were subse- 3 |
