OCR Text |
Show the seeding routine according to C can be answered by simply noting the frequency of occurrence of cloud temperature -20°C on Mt. Harris radiosondes, and multiplying this by the magnitude of seeding effect observed in the warm category. From 165 Mt. Harris radiosondes taken over the past three seasons, the frequency of estimated cloud top temperature -20°C is 60%. Using the 174% increase at Rabbit Ears Pass for the warm temperature category, and making the assumptions that (1) the precipitation data sample is reasonably representative of seasonal precipitation rates, and (2) perfect three-hour predictions of cloud top temperature can be made, the indicated possible overall seasonal precipitation increases from selective seeding could amount to as much as 100% at Rabbit Ears Pass. Since short period variability in cloud top altitude (and thus cloud top temperature) is rather extreme due to transient mesoscale fields of vertical motion, the predictability of cloud top temperature is fairly low. An additional upwind radiosonde station (30-50 miles) could increase the predictability, considerably. A more realistic seasonal increase in precipitation using optimized seeding would likely be of the order of 2 5% to 4~%. In summary, statistical analysis of the stratified 1968-69 data yields significant evidence of the following seeding effects: (1) large positive effects (> 100%) under conditions of westnorthwest to northwest flow aloft when the cloud top temperature was -20°C, and fairly large decreases for cloud tops < -20°C. (2) moderately large precipitation increases (50%) for 550 mb temperature 2: -20°C and westnorthwest to northwest flow, and moderate decreases for 550 nib temperature < -23 °C. , (3) an increase in the frequency of precipitation in the Yampa Valley west, of the ridge (at Lufkin) due to seeded crystals forming at warmer, lower elevations than would occur naturally. On the basis of the above evidence and Mt. Harris radiosonde climatology, and accounting for 80me short range non-predictability of cloud top temperature, it is estimated that optimized seeding would -produce 25% increases of seasonal precipitation at Rabbit Ears Pass. 5. 5 Climatological Evidence of Seeding Effect 5. 5. 1 Studies Using Snow Courses All of the available climatological and snow-course data have been analyzed in an attempt to isolate a positive seeding effect. Steamboat Springs was selected as a control station and a plot of 1 March snow pack water content 300 |