WMOD00293 - Laserfiche WebLink

Home Browse Search

. . ... dispenser. That dispenser, and two satellite dispensers, were controlled by the presence/absence of SL W, wind measurements, and (redundant) air temperature observations. - The automated seeding system had some problems, but they are considered minor and easily correctable. The system generally functioned very well, especially considering that no visits were made to the dispensers once testing started. Some improvements should be made in the data logger program. A more rigid holder for the propane stream temperature sensor would eliminate the cycling problem experienced by the Bald Mountain dispenser. It is recommended that future use of an automated propane dispenser system use simplified criteria. The presence of SL W would continue to be measured by a Rosemount icing rate device well ~p the windward slope. Seeding would commence as soon as the first Rosemount cycle occurred. Seeding would continue for some time (about 2 h) after the last Rosemount cycle in an episode. Wind speed and direction could be monitored but are not believed es~ential because SL W rarely occurred unless wind speed and direction were appropriate for targeting the Wasatch Plateau. (It is anticipated that most north-south oriented mountain ranges would experience similar conditions.) Some propane would be released during essentially unseedable conditions if only SL W presence/absence was used to control seeding. However, the amount of wasted propane is expected to be minor. A thermoelectric generator-battery-inverter combination, as used at the HAS in early 1994, is a practical means of powering a Rosemount icing rate device, a data logger/controller, a propane dispenser and radio gear at an exposed remote location in all weather conditions. This system could be the master station controlling a number of satellite dispensers located at similar high altitude sites crosswind of the master station. All sites should be chosen where local SL W production is expected. If one wanted to be sure that SL W existed at each dispenser, each site could monitor SL W with a Rosemount device. This would be a superior but more costly approach. Propane dispenser testing in California and Utah in recent years has demonstrated the feasibility of a completely automated system that is both reliable and economical. Analysis of the early 1994 physical . seeding experiments should improve understanding of the snowfall-enhancing capability. of propane seeding. Prior research leaves no doubt that propane seeding can markedly enhance ice crystal concentrations with liquid cloud at or below 0 oC. However, it is recommended that the ice crystal yield of the currently-used (in Utah) propane nozzle and release rate be documented. The previously-cited yield values of 1011 to 1012 ice crystals per gram of propane are based on investigations done over two decades ago. These studies used different release rates and nozzles than recently used in California and Utah. It is of obvious interest to test the current design to determine whether yield value are as high as expected. , . Additional key questions to be answered concern ice crystal growth and fallout times downwind of propane dispenser sites. To be effective, propane dispensers need to be within SL W cloud, or at least not far below SLW cloud base where saturation with respect to ice exists. This requires that dispensers be located well up the windward slopes of mountain barriers. Such siting limits the time ( distance) available for ice crystal growth to snowflake sizes-and fallout to the mountain surface. There is concern that this time (distance) may frequently be too limited for significant snowfall to occur before the seeded ice crystals are carried into the lee subsidence zone where sublimation and evaporation occur. , . Another concern with high altitude releases of propane (or AgI) is that crosswind dispersion may be limited, requiring that the crosswind spacing of generators also be limited to avoid unseeded "gaps" between seeding plumes. It may be possible to have greater spacing between AgI generators located further down slope or in upwind valleys thereby requiring fewer seeding sites. Of course, use of lower 67 L