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Retrieval of Raindrop Size Distributions Using Two Doppler Wind Profilers: Model Sensitivity Testing

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  • 1 Cooperative Institute for Research in Environmental Science, Department of Electrical and Computer Engineering, University of Colorado, Boulder, Colorado
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Abstract

The behavior of precipitation is of great importance in obtaining a better understanding of heat transport estimates and global processes in the atmosphere. This paper discusses improvements in an earlier raindrop size distribution model that utilizes two Doppler wind profilers to obtain accurate measurements of rainfall. A UHF Doppler wind profiler provides a precipitation return while a VHF Doppler wind profiler provides vertical clear-air velocities. The model is tested using simulated data. Sensitivity tests examine the model's ability to estimate rainfall characteristics given typical (noisy) Doppler spectra, and the model's sensitivity to atmospheric parameters. Because it is necessary to estimate pressure, temperature, raindrop temperature, and water vapor pressure at the location of the radar volume, the sensitivity tests examine the effects of errors in the estimates of these parameters. Sensitivity testing of the raindrop size distribution model with simulated data indicates model accuracy and reliability and is necessary in the interpretation of results using real data. Testing shows that the model is very capable at estimating even multiple-peaked drop size distributions from noisy UHF spectra. Sensitivity analyses of atmospheric parameters reveal that model results are quite robust, yielding good accuracy for a wide range of atmospheric parameter estimation errors.

Abstract

The behavior of precipitation is of great importance in obtaining a better understanding of heat transport estimates and global processes in the atmosphere. This paper discusses improvements in an earlier raindrop size distribution model that utilizes two Doppler wind profilers to obtain accurate measurements of rainfall. A UHF Doppler wind profiler provides a precipitation return while a VHF Doppler wind profiler provides vertical clear-air velocities. The model is tested using simulated data. Sensitivity tests examine the model's ability to estimate rainfall characteristics given typical (noisy) Doppler spectra, and the model's sensitivity to atmospheric parameters. Because it is necessary to estimate pressure, temperature, raindrop temperature, and water vapor pressure at the location of the radar volume, the sensitivity tests examine the effects of errors in the estimates of these parameters. Sensitivity testing of the raindrop size distribution model with simulated data indicates model accuracy and reliability and is necessary in the interpretation of results using real data. Testing shows that the model is very capable at estimating even multiple-peaked drop size distributions from noisy UHF spectra. Sensitivity analyses of atmospheric parameters reveal that model results are quite robust, yielding good accuracy for a wide range of atmospheric parameter estimation errors.

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