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Wallace E. Howell
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Wallace E. Howell

Recent completion of several research projects into weather modification impacts on the environment provides an opportunity for placing this subject in a new perspective. Studies of physical and biological processes relating precipitation and ecosystem changes show relatively few discernible effects, all of them minor in nature and magnitude. Direct effects of nucleating agents no longer appear consequential. Since no acute problems have surfaced, the focus is likely to shift to possible long-term effects on ecosystems as a whole, where changes associated with natural precipitation gradients and climatic fluctuations provide a model for those to be expected from precipitation management. The weakness of environmental impacts of weather modification compared to the consequences of other human actions renders it unlikely that these impacts will be decisive within a behavioral framework.

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Wallace E. Howell

A simple absorption meter has been built, by using an interference filter, which compares the intensity of incident light in a water-vapor absorption band and in a nearby “window” band. Experiments with the instrument show that it is sensitive to small differences in absorption not only from a direct sunbeam but also from diffuse light scattered by the sky or reflected from clouds. Further observations on clouds are suggested as perhaps being capable of useful interpretation.

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Wallace E. Howell
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Manuel E. López and Wallace E. Howell

Windstorms do great damage in banana plantations near the Sierra Nevada de Santa Marta in Colombia. These plantations, which owe their location to the rainfall maximum caused by convergence in the trade winds as they flow around the mountain massif, suffer most damage from the few most violent tempests and relatively little from the frequent milder squalls, offering the prospect that even slight mitigation of severe storms would be economically rewarding. Most damage was found to be triggered by easterly waves and similar large-scale disturbances, though the windstorms themselves remained purely local. Cloud seeding to attempt reduction of windstorm intensity was undertaken during the 1956 and 1957 seasons on the hypothesis that stimulation of showers early in the diurnal build-up of instability would dissipate some of the instability and reduce insolation at the ground, thus diminishing the intensity of later convective overturning. Comparison of damages during these seeded seasons with those of preceding and subsequent seasons showed a marked reduction in the ratio of severe windstorms to mild ones during the campaign and a reduction perhaps as much 39 per cent in damages, worth several million dollars annually.

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Earl G. Droessler, Wallace E. Howell, Verner E. Suomi, and Helmut Weickmann
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