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<br />. '~ Results of the Shakedown Season for the First Precipitation Augmentation Experiment of the Sierra Cooperative Pilot Project <br /> <br /> <br />)7' <br /> <br />o <br /> <br />t <br /> <br />North <br /> <br />\ <br />\ <br />\ <br />\ <br /> <br />Figure 2. 1'1'1 Plot of Reflectivity on 14 February 1979 at 2044 PST, Speckles> 10 DBZ, Light Contours> DBZ, <br />Heavy Contours> 30 DBZ, Solid> 40 DBZ. <br /> <br />to permit any conclusions. Estimates of the sample size <br />needed to determine if seeding is producing a consistent <br />effects range from 40 cases to over 100. <br />Ground Microphysics - A PMS 2D-C probe has been <br />adapted for use on the SCPP to measure changes in ice <br />crystal concentration and size distributions at the ground. <br />This instrument has great promise for measuring seeding <br />effects which may not be possible with standard precipita- <br />tion gages. <br />Figure 3 shows the ice crystal concentration as a function <br />of time when two CO2 seeding lines were released about <br />40 km upwind of the instrument. The lines were released <br />about 10 minutes apart, perpendicular to the wind, and <br />about 40 minutes upwind of the probe. The cloud type was <br />a uniform, orographic nature rather than the cellular con- <br />vective type of SCPP-l. The relatively uniform background <br />concentration for this type makes the two spikes at 2009 <br />and 2021 Pacific Standard Time produced by seeding easily <br />detectable. <br /> <br />CONCLUSION <br /> <br />The 1981-82 SCPP-l shakedown season adequately <br />tested the instrumentation and procedures for the experi- <br />mental design of an exploratory experiment on cellular con- <br />vection. With some modification to the experimental pro- <br /> <br />cedures, it is concluded that a multi-year experiment start- <br />ing in 1982-83 may be possible. Before a final decision can <br />be made to proceed, statistical evaluation of the period of <br />time needed to detect effects and a benefit cost study must <br />be completed. <br /> <br />LITERATURE CITED <br /> <br />Huggins, A. W., 1981. Classification and Distribution of Radar <br />Echoes for the SCPP: Eighth Conference on Inadvertent and <br />Planned Weather Modification, Reno, Nevada, pp. 36-37. <br />Marwitz,1. D. and R. E. Stewart, 1981. Some Seeding Signatures in <br />Sierra Storms. 1. Appl. Meteor., Vol. 20, No. 20, No. 10, pp. <br />1129-1144. <br />Solak, M. R., Allan, T. Henderson, M. Henderson, S. Pinion, .E. <br />Pinion, S. Barnes, H. Duckering, 1981. SCPP Data Collection <br />and Analysis for the Period 1 July 1980 through 31 August 1981. <br />Interim Progress Report No.3, Atmospherics, Inc., WSBR Con- <br />track No. 9-07-85-Voo, 160 pp. <br />Vardiman, L., 1982. The Design of SCPP-1. A Randomized Pre- <br />cipitation Augmentation Experiment on Winter Cellular Convec- <br />tion in the Central Sierra Nevada. Available from: Bureau of <br />Reclamation, Division of Atmospheric Resources Research, <br />D-1200, P.O. Box 25007, Denver, CO 80225. <br />Vardiman, L. and J. D. Marwitz, 1981. A Scenario for an Explora- <br />tory Seeding Experiment on Post-Frontal Convection in the <br />Sierra Cooperative Pilot Project. Eighth Conference on Inad- <br />vertent and Planned Weather Modification. Reno, Nevada, pp. <br />82-83. <br /> <br />421 <br />