Acceleration to Terminal Velocity of Cloud and Raindrops

P. K. Wang Department of Atmospheric Sciences, University of California, Los Angeles 90024

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H. R. Pruppacher Department of Atmospheric Sciences, University of California, Los Angeles 90024

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Abstract

A theoretical method is given which allows computing the acceleration to terminal velocity of cloud and raindrops at various levels in the atmosphere. For drops of equivalent radius 800 μm ≤ a0 ≤ 3500 μm our theoretical predictions were found to agree well with the results of an experimental study carried out in the UCLA Rain-Shaft. For drops of 20 μm ≤ a0 ≤ 80 μm our theoretical predictions were found to agree well with the experimental results of Sartor and Abbott (1975). Experiment and theory indicate that in air of 1000 mb and 20°C, drops of a0 > 1000 μm need distances of at least 12 m to accelerate to terminal velocity.

Abstract

A theoretical method is given which allows computing the acceleration to terminal velocity of cloud and raindrops at various levels in the atmosphere. For drops of equivalent radius 800 μm ≤ a0 ≤ 3500 μm our theoretical predictions were found to agree well with the results of an experimental study carried out in the UCLA Rain-Shaft. For drops of 20 μm ≤ a0 ≤ 80 μm our theoretical predictions were found to agree well with the experimental results of Sartor and Abbott (1975). Experiment and theory indicate that in air of 1000 mb and 20°C, drops of a0 > 1000 μm need distances of at least 12 m to accelerate to terminal velocity.

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