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Can polarisation help NEXRAD to provide better rainfall estimates?

Anthony Illingworth

University of Reading

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It will be difficult to use the polarisation parameters on Nexrad for rainrates below 10 mm/hr because the signals are small and noisy. However, we have found that by looking at the distribution of the Z and the noisy differential reflectivity (ZDR) signals over a 5 km square area we are able to derive the raindrop concentration, Nw, quite accurately and hence compute the value of "a" which could be used in the empirical Z = aR 1.5 relationship. We find remarkable consistency with the Nw derived from a coincident profiler thus confirming the precision and validity of the Z/ZDR technique. Traditionally rainfall rates from radar are evaluated using gauges or a disdrometer, but the disdrometer yields rather different values of Nw, thus demonstrating that the smaller sampling volume of ground based gauges or disdrometers limits their use for evaluating rainfall algorithms.

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Wednesday, July 26, 2006
2:00 PM (Refreshments at 1:50 pm)
PSD-South Conference Room (1D403)

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