OCR Text |
Show periods of seeding effect. Additional replica series analyzed only for crystal habit and size also support this conclusion. In summary, from all detailed case studies made (including some for previous years of pulsed seeding from Emerald Mountain) it can be concluded that: ( 1) Significant quantities of seeding material were present in target area precipitation, in timing and location agreement with calculated occurr ences of seeding effect. (2) Seeding material frequently produced many small hexagon9-l plate snow crystals, and occasionally some dendrites. (3) Statistical testing for overall seeding influence on precipitation rates, when the data were stratified according to cloud top temperature, showed statistically significant i:qcreases due to seeding for cloud top temper-20°C. ature (4) In several individual cases with good data quality and relatively uncomplicated natural precipitation rate traces, a positive seeding effect was clearly evident. (5) In most cases, the largest seeding effect on precipitation when seeding from Emerald Mountain probably occurred downwind of the Park Rangedata network, perhaps ·affecting precipitation in downstream orographic ally favorable areas (see Section 5. 5). This conclusion is based on plume diffusion and crystal trajectory calculations in conjunction with the - l 5°C isotherm mean elevation. (6) Mt. Harris ground releases frequently deposited seeding material in precipitation as far west as Emerald Mountain, and produced snow crystals at Rabbit Ears Pass with AgI particle centers. (7) Airborne seeding along predetermined tracks spreads significant quantities of seeding material over all of the target area in most cases. This conclusion is supported by measurements of silver content in precipitation, and also by AgI particles microscopically visible at the centers of individual snow crystal replicas. (8) Seeding effects from only a few minutes to an hour of seeding can last for three to four hours. (9) Frequent sampling of vertical profiles of wind, temperature, a~d humidity are mandatory for evaluation of seeding effects with such short per10d seeding events. 293 |