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Manuel E. López

Various special methods of analyzing raobs in the tropics for forecasting purposes are tested and a combination of the best features found is recommended; this technique consists in plotting the 24-hour change of contours of the isobaric surfaces on a time or space cross-section. Some of the difficulties and limitations of such methods are pointed out.

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Wallace E. Howell and Manuel E. López

Abstract

With the most severe drought on record in its eighteenth month, causing severe damage and hardship in Puerto Rico, several large private concerns and government agencies interested in water decided that the immediate need for water greatly outweighed the uncertainties involved in cloud seeding, and collaborated to sponsor a program of rainfall stimulation. Operations of an emergency nature began 26 April and continued until 18 July 1965.

The result is evaluated by estimating the amount of rain that would have fallen if no seeding had been done, from the average rainfall per rainy day during a 19-year (unseeded) period. This analysis indicated an increase of 2.69 inches, equivalent to a 14 per cent increase nominally significant at the 10 per cent level.

No formal evaluation of the economic outcome is offered, but crop reports suggest that the cloud-seeding program returned value many times its cost, hence justifying the undertaking in the face of the uncertainties involved.

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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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Manuel E. López and Wallace E. Howell

Abstract

Diurnal air tides that carry Pacific maritime air eastward through passes and over lower portions of the continental divide are remarkably similar over long stretches of the Andes from northern Chile to central Colombia, embracing both desert and jungle climates on the Pacific Coast. Even where the maritime air is at its warmest, it overflows the divide as a cold current producing katabatic flows down the east slope of the range and often producing hydraulic jump phenomena in the valleys immediately to the east. The significance of this pattern for the rainfall climate of western Colombia is discussed.

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Manuel E. López and William W. Vickers

Abstract

A technique has been developed to correct rocket tracking radar inputs in near real time (maximum computing time of 100 msec) for refractive effects, by iterating twice an approximate closed-form solution for an exponentially stratified model. Maximum computational discrepancies for a test atmosphere between the results using this technique and those using an accurate numerical integration of the ray-tracing equations were under 3 m for the range error and 0.2 mrad for both the bending and the elevation errors. The technique works well for any initial antenna elevation angle, including zero and negative values, and for all practical radar ranges.

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