Microphysical Interpretation of Multi-Parameter Radar Measurements in Rain. Part II: Estimation of Raindrop Distribution Parameters by Combined Dual-Wavelength and Polarization Measurements

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  • 1 Illinois State Water Survey, Champaign, IL 61820
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Abstract

The radar reflectivity weighted mean axis ratio R¯ and the variance of the axis ratio distribution σR2 of an ensemble of raindrops can be estimated from polarization radar measurements. If the shape function relating axis ratio to drop size is known or measured, then these quantities may be transformed into the radar reflectivity weighted mean diameter D and, in the case of quiescent drops, into the variance of the raindrop size distribution σD2. Although these parameters are of intrinsic meteorological interest, estimates of the rainfall rate in still air R0 and of liquid water content W can also be constructed. In principle, estimates using both D¯ and σD2 appear, potentially, to be more accurate than estimates based only on D¯. Realization of this potential improvement probably depends on the development of techniques to extract that component of σD2 arising solely from the raindrop size distribution.

Abstract

The radar reflectivity weighted mean axis ratio R¯ and the variance of the axis ratio distribution σR2 of an ensemble of raindrops can be estimated from polarization radar measurements. If the shape function relating axis ratio to drop size is known or measured, then these quantities may be transformed into the radar reflectivity weighted mean diameter D and, in the case of quiescent drops, into the variance of the raindrop size distribution σD2. Although these parameters are of intrinsic meteorological interest, estimates of the rainfall rate in still air R0 and of liquid water content W can also be constructed. In principle, estimates using both D¯ and σD2 appear, potentially, to be more accurate than estimates based only on D¯. Realization of this potential improvement probably depends on the development of techniques to extract that component of σD2 arising solely from the raindrop size distribution.

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