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Alan I. Weinstein

Abstract

A one-dimensional, steady-state cumulus model is used to evaluate the climatological potential for precipitation augmentation by ice-phase seeding of isolated cumulus clouds in the western United States using data for May-September 1967 and 1968. Atmospheric conditions favorable for seeding with ice nuclei in order to initiate thermodynamic instability occurred on approximately 25% of the days. On these days, the calculations indicated that seeded cumulus clouds could have been made to produce an average of approximately 50% (0.3 inch) more precipitation than their non-seeded neighbors. Decreases averaging approximately 0.1 inch per cloud were calculated to occur on approximately 20% of the days.

The areas of the western United States that would have been most favorable for ice-phase seeding of isolated cumuli during the two years of the study were the southwestern states of Arizona, New Mexico and Texas. The least favorable areas were in the plains states of Kansas, Nebraska and South Dakota.

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Alan I. Weinstein

Abstract

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Alan I. Weinstein

Abstract

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Alan I. Weinstein

Abstract

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Alan I. Weinstein

Abstract

A one-dimensional, time-dependent numerical model of cumulus convection is presented. The model considers the processes of horizontal mixing, evaporation, precipitation generation and freezing, as well as the standard thermodynamic and dynamic processes in isolated cumuli. The initial calculations show that: 1) the vertical velocity and liquid water content undergo coupled damped oscillations in time; 2) the rate at which precipitation-sized drops are formed and grow by collection are not sensitive parameters in the amount of rain which falls from the clouds; 3) the amount of liquid water in the form of cloud droplets that must be present in the cloud before a few large drops can be developed is a crucial parameter in determining the amount of rain which falls from the clouds (the higher the threshold cloud liquid water content, the lower the ultimate rainfall amount); and 4) the freezing time and precise ice-nucleation temperature affect the amount of rain that falls from the cloud in a way often very different from the way they affect the cloud-top height.

Trial runs with the model agree well with observations in the two cases tried.

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Alan I. Weinstein

Abstract

Hourly surface weather observations are combined with air traffic records to calculate projected utilization of operational warm fog dispersal systems at 15 Air Force bases in the United States and Europe, and at one civilian airport in California, Los Angeles International (LAX). It is projected that between 0.8 and 2.7% of the flights at the airports in the United States and between 4.8 and 7.1% of those at the European bases are adversely affected by warm fog in an average year. In most cases these percentages represent between 300 and 500 flights per year at the Air Force bases in the United States, approximately twice that amount of traffic at the bases in Europe, and approximately ten times that number of flights at LAX.

A similar study sponsored by the FAA allowed comparable projections to be made for 40 additional civilian airports. Of the 21 civilian airports with the highest projected utilization of warm fog dispersal systems, it was found that the percentage of affected landings was generally less than one-half of the Air Force bases, but the total number of such landings was generally as high, and in many cases considerably higher.

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Alan I. Weinstein and Frederick Sanders

Abstract

No abstract available.

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Alan I. Weinstein and James R. Hicks

Abstract

Experiments have been performed under controlled and free environment conditions to determine the technical feasibility of using the cooling resulting from the adiabatic expansion of compressed air to initiate ice crystal production in a supercooled fog. These experiments have shown that for most supercooled temperatures, approximately 103 cm3 of air when compressed to 60 psig and released through a supersonic nozzle will produce the same number of ice crystals as does the evaporation of 1 cm3 of liquid propane. It is estimated that a compressed air supercooled fog dispersal system would consume approximately 6% of the hydrocarbon fuel presently consumed by operational systems using liquid propane spray.

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Alan I. Weinstein and Bernard A. Silverman

Abstract

A two-dimensional Eulerian model of warm fog dispersal by airborne hygroscope particle seeding is used to evaluate some practical aspects of urea seeding at airports. It is found that although turbulence and wind shear reduce the effectiveness of single-line seeding to a point where it is of no practical value, seeding over a wide area (1−10 mi2) can result in practically useful visibility improvements in the approach zone and over the runway of airports.

The quantity of material and the cost of the wide-area seeding technique depend upon fog intensity, fog type, and cross-runway wind speed. For typical fog, approximately 80,000 lb hr−1 of urea costing $40,000 per hour are needed to keep the visibility above ½ mi. The figures are reduced to approximately 36,000–58,000 lb and $18,000–29,000 per hour, respectively, if the visibility needs only to be raised to ¼ mi.

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Bruce A. Kunkel, Bernard A. Silverman, and Alan I. Weinstein

Abstract

Thermal fog dispersal tests were conducted by the Air Force Cambridge Research Laboratories during July 1972 at Vandenberg AFB, California. The experimental heating system consisted of an array of passive liquid propane burners that were arranged in four lines perpendicular to the prevailing wind. An instrumented 200 ft tower and a lidar were used to monitor the effects of the tests on the foggy environment.

The heating tests were designed to simulate fog dispersal operations at an airport under cross-runway wind conditions. The effect of wind speed and heat output on the temperature, visibility and turbulence structure of the environment are discussed. The test results confirmed the earlier findings of the British FIDO program during WW II with respect to the characteristic temperature rise pattern for a cross-wind situation. The program documented visibility improvements in the heat plumes that could only be inferred from the published FIDO temperature rise data. Extrapolating the results of these experiments to a similar system installed at an airport, it appears that the visibility improvements that were achieved in the experiments would always be adequate for Category 2 (100 ft decision height, ¼ mi visibility) and 3A (no decision height, ⅛ mi visibility) landing operations. Category 1 (200 ft decision height, ½ mi visibility) landing conditions could be achieved by increasing the heat output of the burners.

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