Laserfiche WebLink
<br />I <br /> <br />our understandi ng of preci p'itati on develop- <br />ment in natural and'seeded clouds. It spe- <br />cified in advance and attempted to verify by <br />observations during the course of the experi- <br />ment each step leading to additional precipi- <br />tation from seeding. It was similar in <br />approach to experiments conducted by Braham <br />et a1., (1957) and Bethwaite et a1., (1966) <br />but more of the steps in the chain of physi- <br />cal events could be included because of <br />recent developments in observing, measuring <br />and real-time data processing capabilities. <br /> <br />Among the important concepts that were <br />employed, some for the first time in weather <br />modification, in designing, executing and <br />evaluating HIPLEX-l are the following (Smith <br />et a 1., 1984): <br /> <br />1. The investigation was carried <br />out in successive stages, with: a) an <br />initial exploratory stage to develop <br />an understanding of the clouds of the <br />area, upon which the design of a phy- <br />sically meaningful seeding experiment <br />could be based, b) preliminary <br />calibration seeding trials to develop <br />a methodology for executing the <br />seeding operation as required by the <br />physical hypothesis, and c) an <br />exploratory randomized seeding experi- <br />ment (HIPLEX-l) on individual, small <br />clouds to test the seeding hypothesis. <br />It was planned that follow-on experi- <br />ments would be conducted that would <br />move up the scale to larger cloud <br />systems as increased understanding <br />permitted, leading ultimately to an <br />area seeding experiment; however, this <br />is not yet possible for both scien- <br />tific and support reasons. <br /> <br />2. A detailed multi-step physical <br />hypothesis was formulated with empha- <br />sis on expected differences between <br />seeded and non-seeded clouds. For <br />each step of the hypothesis, response <br />variables capable of being measured <br />were defined, so that the expected <br />differences could be monitored. For <br />the response variables associated with <br />each step, indications were provided <br />of how, when and where the <br />seed/non-seed differences were to be <br />measured. This aspect is particularly <br />important because it provides for <br />determining not only whether the <br />seeding produces increased rainfall, <br />but also whether the physical mecha- <br />nism is correctly understood. <br /> <br />3. Physical measurements of the <br />characteristics of candidate clouds <br />were made and analyzed in real-time to <br />determi ne thei r suitabil ity as experi - ' <br />mental units. <br /> <br />4. Provisions ~!ri made for a statistical <br />evaluation and a complementary physical <br />evaluation of the experiment. The sta- <br />tistical evaluation of the physic.a1ly <br />based experiment focused on establishing <br />proof of changes due to seeding and on <br />verifying the hypothesized physical <br />sequence of events leading to the changes <br />(Mielke et a1., 1984). The physical eva- <br />luation focused Cn case studies to estab- <br />lish the cause-and-effect relationships, <br /> <br />~-":'i:~,z~a~e) - <br /> <br />or'lack thereof, of any-seedfn'g-produced <br />modifications to the cloud and its physi- <br />cal mechanisms (Cooper and Lawson, 1984). <br /> <br />Because of the experimental approach used in <br />HIPLEX-1, it was pOSSible to determine where. <br />how and why seeded clouds behaved di fferent 1y <br />from natural clouds and, more important, <br />behaved differently than hypothes i zed. It <br />was possible to provide a better <br />understanding of basic cloud processes and <br />their response to seeding in spite of the <br />limited data set that was available. <br /> <br />7. Future <br /> <br />The SCPP. CRAD? and CREST programs are based <br />on the experimental strategy introduced by <br />HIPLEX-1. Indeed. we have probably seen the <br />last of the so-called "black-box" experiments <br />which 'try to relate cloud seeding to precipi- <br />tation on the ground while ignoring the <br />complex chain of intermediate processes~ Our <br />inability to understand the physical reasons <br />underlying the FACE-1 and FACE-2 experimental <br />results and their implications is ample evi- <br />dence of the limitations of the "black-box" <br />experimental approach. Credibility of the <br />science of weather modification depends on <br />understanding the physical reasons for the <br />results of all experiments. whether they <br />yield positive. negative. or no effect. As <br />Braham (1981) suggests it is likely that the <br />primary emphasis of future scientific weather <br />modification field experiments in the United <br />States will be improving understanding of <br />basic microphysical and dynamical proce!ises <br />in clouds. interactions between them and, <br />their reactions to seeding in a variety of <br />cloud types and climatic regions. The <br />distinction between seeding for microphysical <br />effects only (static seedi ng) and dynamical <br />effects only (dynamic seeding) will likely <br />disappear as we clarify the role of environ- <br />mental and cloud dynamics in controlling pre- <br />cipitation development and the effects of <br />cloud microphysics on these dynamical pro- <br />cesses. <br /> <br />8. References <br /> <br />, Barnston. A. G.. W. L. Woodley. J. A. , <br />Flueck. and M. H. Brown. 1983: <br />Florida Area Cumulus Experiment's <br />second phase (FACE-2). Part I: <br />The experimental design. implemen- <br />tation and basic data. J. C1im. <br />~ Meteor.. 22. 1504-1528.- <br />Bethwaite. F. D.. E. J.. Smith. J. A. <br />Warburton. and K. J. Heffernam. 1966: <br />Effects of seeding isolated cumulus <br />clouds with silver iodide. <br />J. Appl. Meteor.. 5. 513-520. <br />Blumenstein. R. R., W. G. Finnegan. and L. 0 <br />Grant, 1983: Ice nucleation by silver <br />iodide-sodium iodide - a reevaluation. J. <br />Wea. Mod.. 15, 11-15'. - <br />Braham, R. R.,Jr.. 1960: Physical properties <br />of clouds. J. lrrig. Drain. Div.. Proc. <br />ASCE, 86, 111-119. - <br />Braham. R. R..Jr.. 1981: Designing cloud <br />understanding. Bull. Amer. Meteor. Sec., <br />62, experiments for physica'155-62. <br />Braham, R. R..Jr.. L. J. Battan. and H. R. <br />. Byers, 1957: Artificial nucleation of <br />cumulus clouds. in cloud and weather'modi- <br />fication. Meteor. Mono.. 2. 47-85. <br /> <br />J_ <br /> <br />, <br />C:C <br /> <br />:!' .!t 1 <br />:t';) i !'"Ii' <br /> <br />~"~1"~~ <br />