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Last modified
7/28/2009 2:35:20 PM
Creation date
3/11/2008 11:30:28 AM
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Weather Modification
Title
Harold D. Orville Symposium - Forty Years of Modeling Clouds and Weather Modification
Date
4/26/2003
Weather Modification - Doc Type
Report
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<br />I <br /> <br />I <br />I <br /> <br />Numerical Simulation of Cloud Seeding <br /> <br />Richard D. Farley <br />Institute of Atmospheric Sciences <br />South Dakota School of Mines and Technology <br />Rapid City, South Dakota <br /> <br />I. INTRODUCTION <br /> <br />Harry Orville has long been a powerful advocate <br />for weather modification, and a major proponent of the <br />use of numerical simulation of the possible effects of <br />weather modification activities. Numerical cloud <br />models have been applied to various aspects of the <br />weather modification problem for approximately 40 <br />years, dating back to the one-dimensional steady-state <br />models of Simpson et al. (1965), Simpson and Wiggert <br />(1969, 197]), and Hirsch (1972). These models did a <br />reasonably good job of predicting changes in cloud top <br />height induced by ice-phase seeding. However, these <br />simple models were incapable of representing the <br />complete cycle of precipitation formation, evolution <br />and fallout, which require time-dependent multi- <br />dimensional frame-works with interacting microphysics <br />and dynamics. Harry Orville has been a major player in <br />the application of cloud models to weather modification <br />research as it has evolved over the years. He has always <br />argued for the realistic treatment of cloud and <br />precipitation processes within coupled field-of-flow <br />models. As such, much work in this area has been <br />conducted in tandem with efforts at model verification <br />through comparison to cloud observations and efforts to <br />improve the representation of microphysical processes. <br /> <br />Reviewing the Institute of Atmospheric Sciences <br />(IAS) author files, I counted more than 100 articles, <br />(refereed publications, conference papers, and reports) <br />pertaining to numerical simulations of various forms of <br />cloud-scale weather modification that were authored or <br />coauthored by Harry Orville. To that w~ can also add <br />over 30 theses supervised by Dr. Orville plus an <br />additional 10 articles by other members of the modeling <br />group that were either sponsored. or inspired by him. <br />That is a tremendous legacy in this one subject area <br />alone. <br /> <br />This interest in weather modification has not been <br />limited to conventional cloud seeding. It has also <br />included inadvertent weather modification topics such <br />as the effects of air pollution. on clouds and <br />precipitation (as in Hjehrtfelt et al., ]978, and Sarma, <br />1986), and the <br />effects of excess heat and vapor from power plant <br />complexes on clouds and severe storms (as in Orville et <br />al., 1981),. non-traditional cloud seeding such as the <br /> <br />Author address: Mr. Dick Farley, lAS, SDSM&T, <br />501 E. St. Joseph Street, Rapid City, SD 5770]-3995. <br /> <br />effects of carbon black dust on convection (Chen and <br />Orville, 1977), and the release of ions by chaff seeding <br />or ion-wire experiments in efforts to reduce electric <br />fields (Helsdon, 1980; Helsdon et al., 1988). <br /> <br />I <br /> <br />I <br /> <br />In addition to the vast set of studies produced <br />directly by Dr. Orville and associates at lAS, there have <br />been numerous studies conducted by colleagues around <br />the world who have been inspired by the efforts of Dr. <br />Orville. In' the comments that follow, I shall restrict <br />myself to a review of numerical simulations of planned <br />weather modification by cloud seeding. I will also <br />concentrate on research produced by Dr. Orville and <br />associates at lAS, realizing full well that many other <br />researchers have contributed greatly to the field. For a <br />more broadly-based discussion of the role of cloud <br />modeling in weather modification see Orville (1996). <br /> <br />I <br />I <br /> <br />I <br /> <br />The reproducible environment of the computer <br />provides an ideal laboratory for testing the effects of <br />cloud seeding on clouds and cloud systems. The virtual <br />reality of the computer creates clouds which are <br />identical up to the time of treatment. This is in stark <br />contrast to the irreversible nature of real clouds. Once <br />treated in the field it is impossible to say with any <br />certainty what would have happened had it not been <br />treated or if it had been treated differently. <br />Unfortunately, this magical world of numerical <br />simulations is at the mercy of the accuracy and realism <br />of the particular model applied. <br /> <br />I <br />I <br /> <br />I <br />I <br /> <br />The degree of realism in numerical simulations of <br />cloud seeding has improved over time as a direct result <br />of increased computer performance and increased <br />microphysical sophistication within increasingly more <br />realistic dynamic frameworks. The goals of the <br />simulations have evolved as well. Originally, the <br />simulations were conducted in hopes of determining a <br />range of possible responses to seeding. Over time there <br />has been increasing emphasis on determining the <br />quantitative nature of the response. Cloud models of <br />varying complexity are employed in a variety of <br />applications in the field of weather modification. They <br />include hypothesis development and testing, assessment <br />of seeding potential, experimental design for the <br />conduct of field operations, operational decision- <br />making, project evaluation, and understanding of <br />seeding effects. The various models developed by the <br />IAS have addressed all of these applications to some <br />extent, but our cloud seeding simulations have tended <br />to concentrate on evaluating various hypotheses, <br /> <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />I <br /> <br />14 <br /> <br />I <br />
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