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Joanne Simpson
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Joanne Simpson

Abstract

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Joanne Simpson

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Joanne Simpson

Abstract

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Joanne Simpson
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Joanne Simpson

Abstract

Downdrafts are postulated as a primary linkage dynamically seeded invigorated cloud towers and those events near and below cloud bases which cause enhanced inflow, new tower growth leading to cloud expansion, and frequent merger with neighboring clouds. Evidence is taken from two series of seeding experiments on relatively isolated cumuli in the tropics and subtropics, and combined with evidence derived from observational material on downdrafts collected since the late 1960's. Because all the events discussed can occur naturally, postulates concerning the effects of the seeding and their detection are proposed. It is suggested how acceleration of the cloud tops invigorated by seeding can lead to enhanced dynamic entrainment, increased evaporation, and hence to more rapidly formed and stronger downdrafts than would be the case without seeding. Supporting model results on natural clouds are cited.

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Joanne Simpson
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Joanne Simpson

Abstract

The scientific and technological aspects of weather modification are addressed, emphasizing the need for physical understanding, sequential development, predictor variables and an interdisciplinary approach.

The experience of the successful experiments in weather modification such as Climax, Israel and Florida single cumuli have shown the importance of two-phase development, namely, exploratory and confirmatory. A decision ladder to screen out unfavorable cases and/or select between treatments must be optimally based on concepts, numerical simulation and measurement. Cooperation between the academic, government and private sectors in these endeavors will optimize use of people and resources. All these steps together should improve the credibility of weather modification in the scientific community and protect against the present fragility suffered by many operational programs.

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Joanne Simpson

Abstract

In the summer of 1965, a series of tropical cumulus cloud experiments was carried out by Project Stormfury, a joint program of the U. S. Navy and Environmental Science Services Administration. Of twelve clouds seeded with tops colder than −5C, eight grew an average of 10,600 ft following seeding. This is a case study of one of these eight clouds; it was seeded at 25,000 ft (absolute altitude) and grew to about 36,000 ft.

Four instrumented aircraft penetrated the cloud in a stack, at levels from cloud base to about 20,000 ft. A heavily radar equipped “Command” plane controlled the experiment, circling the cloud at a distance of about 25 mi. This paper documents the radar and photographic history of the cloud, mainly as determined from the command aircraft. It is intended to aid in interpretation of the cloud physics measurements provided by the penetrating aircraft, particularly that of the Naval Research Laboratory. The N.R.L. aircraft made repeated traverses through the cloud at 18,000 ft (absolute altitude; 17,000 ft pressure altitude) in the temperature range −3 to −5C. It measured temperature, humidity, and hydrometeor structure, once before and several times after seeding. Conversion from largely water to largely ice was observed in a portion of the cloud together with some interesting temperature increases. This study attempts to relate the seeding effects and internal physical changes to the overall dynamic processes as deduced from radar and photography.

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JOANNE SIMPSON

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This study is based on the radar-evaluated rainfall data from 52 south Florida cumulus clouds, 26 seeded and 26 control clouds, selected by a randomization procedure. The fourth root of the rainfall for both seeded and control populations was well fitted by a gamma distribution for probability density. The gamma distribution is prescribed by two parameters, one for scale and one for shape. Since the coefficient of variation of seeded and control cloud populations was the same, the shape parameters for the two gamma distributions were the same, while the seeded population's scale parameter was such as to shift the distribution to higher rainfall values than the control distribution. The best-fit gamma functions were found by application of the principle of maximum entropy.

Specification of tractable distributions for natural and modified rainfall populations provides an important prerequisite for the evaluation of seeding effects by Bayesian statistics, a continuing objective in the Experimental Meteorology Laboratory cumulus seeding programs.

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