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DROP-SIZIE HISTORY DURING A SHOWER

David AtlasAir Force Cambridge Research Center

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Vernon G. PlankAir Force Cambridge Research Center

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Abstract

A sequence of five closely spaced raindrop samples taken during the passage of a shower displayed approximate monodispersity in each sample, and drops decreasing to drizzle size with time. Correlations of median volume diameter and of liquid-water content with rain intensity agree very well with previously established empirical relations, except for the very first drops. However, values of reflectivity (Z = ∑Nd6) are approximately half those predicted by Z = 200 R1.6, due primarily to the narrow drop-size spectra. Such variations in spectrum width may be accounted for by varying the coefficient of the Z-R relation.

The smallest particles are shown to originate at the very edge of the shower, having evaporated during their fall. The largest particles originate toward the inner portion of the shower, and probably grow to some extent by coalescence in the cloud before evaporating slightly underneath it. All the drops appear to have originated above the melting level.

Abstract

A sequence of five closely spaced raindrop samples taken during the passage of a shower displayed approximate monodispersity in each sample, and drops decreasing to drizzle size with time. Correlations of median volume diameter and of liquid-water content with rain intensity agree very well with previously established empirical relations, except for the very first drops. However, values of reflectivity (Z = ∑Nd6) are approximately half those predicted by Z = 200 R1.6, due primarily to the narrow drop-size spectra. Such variations in spectrum width may be accounted for by varying the coefficient of the Z-R relation.

The smallest particles are shown to originate at the very edge of the shower, having evaporated during their fall. The largest particles originate toward the inner portion of the shower, and probably grow to some extent by coalescence in the cloud before evaporating slightly underneath it. All the drops appear to have originated above the melting level.

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