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<br />t1f -~ <br /> <br />Reprinted from. Preprint Volume: Conference on Sierra <br />Nevada Meteorology, June 19-21, 1978, S. Lake Tahoe, <br />Calif. Published by American Meteorological Society, <br />Boston, Mass. <br /> <br />PRELIMINARY METEOROLOGICAL MEASUREMENTS <br />IN SUPPORT OF THE SIERRA COOPERATIVE PILOT PROJECT <br /> <br />Lalrry Vardiman <br />U. S. BUireau of Reclamation <br />Denver, CO <br /> <br />1. INTRODUCTION <br /> <br />The Sierra Cooperative Pilot Project (SCPP) <br />is part of the Bureau of Reclamation's Project <br />SKYWATER. The objectives of the SCPPare to <br />develop a better understanding of the physical <br />processes of precipitation formation and to <br />identify those conditions that provide the <br />best potential for winter precipitation <br />augmentation in the Sierra Nevada. These <br />objectives include improving current operational <br />cloud seeding methods, transferring the <br />techniques and results to concerned groups, <br />and enhancing public confidence in their use. <br />A design for a long-term research experiment <br />is currently being formulated. One or more <br />major hypotheses with many peripheral hypotheses <br />will be tested. <br /> <br />A prolonged period (approximately 5 years) of <br />randomized seeding is expected to be necessa~( <br />to adequately evaluate the results of a given <br />seed i ng hypothes is or set of seed i ng hypothesl~s. <br />It is apparent that an improved understanding <br />of natural precipitation mechanisms and <br />transport and diffusion characteristics in <br />Sierra Nevada storms should precede a final <br />design for testing seeding hypotheses. <br />Understanding about certain cloud processes <br />is not sufficiently clear to develop sharply- <br />defined hypotheses. Certain cloud seeding <br />procedures for intrOducing artificial nucleants <br />and techniques for the measurement of seeding <br />effects also require further examination. <br /> <br />This paper will discuss some of the more <br />important questions which need resolution and <br />the preliminary studies that have been under- <br />taken to answer them. <br /> <br />2. IMPORTANT QUESTIONS <br /> <br />Many questions should be answered before a <br />new long-term randomized cloud seeding experi- <br />ment is initiated in the Sierra Nevada. <br />However, some are more critical than others. <br />It would take many years to adequately under- <br />stand all of the important processes occurri nl~ <br />in Sierra Nevada storms. If the critical <br />questions can be answered with some acceptabll~ <br />degree of confidence, then many of the remain- <br />ing unknowns can be studied during the experi- <br />ment proper. This approach carries some risk <br />that not all of the important questions have <br />been identified and changes in the experiment <br />will 'be required as it proceeds. However, <br />this uncertainty will always exist in any <br />experiment and one must reach an acceptable <br />level of risk before proceeding. <br /> <br />The following five questions have been identi- <br />fied as the most important and require greater <br />knowledge than presently exists before the <br /> <br />randomized experiment is initiated. These <br />five questions should be answered in sequence. <br />They are very general and are subdivided into <br />more specific subquestions. <br /> <br />1.1 What are the natural microphysical <br />and dynamical characteristics of <br />Sierra Nevada storms? <br /> <br />Where do ice crystals form in <br />the cloud, at what tempera- <br />ture, and in what concentrations? <br />Is ice crystal multiplication <br />occurring and to what degree? <br />What is the role of riming? <br />What is the natural cloud <br />droplet and ice crystal size <br />spectra? <br />Are coalescence and aggregation <br />mechanisms important? <br />How efficient are orographic <br />clouds, convective cells, and <br />convective bands in forming <br />precipitation? <br />How are the horizontal and <br />vertical wind fields related <br />to location on the barrier and <br />to stability? <br />Where and to what degree is <br />conditional instability re- <br />1 eased? <br />How do convective bands and <br />postfrontal instability react <br />with the general storm dynamics? <br /> <br />1.2 Are natural storm characteristics <br />conducive to cloud seeding? <br /> <br />a. <br /> <br />b. <br /> <br />c. <br />d. <br /> <br />e. <br /> <br />f. <br /> <br />g. <br /> <br />h. <br /> <br />i. <br /> <br />a. Do deficiencies in ice crystal <br />concentration occur in regions <br />of a cloud where added crystals <br />would be beneficial in increasing <br />precipitation? <br />b. Do regions of high liquid <br />water content occur which <br />could be nucleated by cloud <br />seeding? <br />c. Does significant riming of ice <br />crystals occur? <br />d. Do regions of instability <br />exist which could be released <br />by seeding? <br />e. Do seedable regions exist in <br />locations where sufficient <br />time and space allow targeting <br />of additional precipitation on <br />the mountain barrier? <br /> <br />1.3 How should seeding be carried out? <br />a. Where are the seedable locations <br /> <br />160 <br />