Effect of Deviations from the Marshall-Palmer Drop Size Distribution on the Calculation of Vertical Air Velocity by Rogers's Method

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  • 1 National Institute for Telecommunications Research, Johannesburg, South Africa
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Abstract

In 1964, R.R. Rogers proposed a method for estimating vertical air velocity in rainfall which is based on the Marshall-Palmer raindrop size distribution. Many investigators have shown that there are deviations from the Marshall-Palmer distribution such that the intercept N0, and the shape may vary. Essential to Rogers' method is the relationship between reflectivity Z and Doppler fall velocity . A numerical method has been used to obtain versus Z relationships for raindrop size distributions different from those of Marshall and Palmer and to compare these with results obtained using Rogers's method. Thus errors that are likely to occur in estimating vertical air motions have been evaluated and are shown to be a maximum of 1.4 m s−1.

Abstract

In 1964, R.R. Rogers proposed a method for estimating vertical air velocity in rainfall which is based on the Marshall-Palmer raindrop size distribution. Many investigators have shown that there are deviations from the Marshall-Palmer distribution such that the intercept N0, and the shape may vary. Essential to Rogers' method is the relationship between reflectivity Z and Doppler fall velocity . A numerical method has been used to obtain versus Z relationships for raindrop size distributions different from those of Marshall and Palmer and to compare these with results obtained using Rogers's method. Thus errors that are likely to occur in estimating vertical air motions have been evaluated and are shown to be a maximum of 1.4 m s−1.

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