11B.2

**Radar Rainfall estimation using different Polarmetric Algorithms**

Alexander V. Ryzhkov, CIMMS/Univ. of Oklahoma, Norman, OK; and T. J. Schuur and D. S. Zrnic

The polarimetric algorithm for rainfall estimation based on the power relation between rain rate R and specific differential phase K_{DP}
R=A K_{DP}^{b}
tends to underestimate / overestimate rainfall if small / large drops dominate the drop size distribution (DSD), although to a lesser degree than the conventional algorithm utilizing radar reflectivity factor Z.

In order to mitigate effects of DSD variability, we suggest the extension of the algorithm R(K_{DP}) with the coefficient A depending on differential reflectivity ZDR averaged over sufficiently large spatial / temporal domain. Different functions A(Z_{DR}) are recommended for light, moderate, and heavy rain. These functions have been derived empirically by comparing one-hour rain accumulations obtained from the Cimarron polarimetric radar and 42 gauges comprising a dense micronetwork in Central Oklahoma. Twenty rain events have been examined.

The use of average values of Z_{DR} instead of point Z_{DR} estimates greatly reduces the influence of statistical errors in Z_{DR} measurements on the overall performance of the suggested algorithm. The result is a much less biased estimate of rainfall compared to the algorithm R(K_{DP}) without noticeable increase in statistical errors.

We have compared also polarimetric variables measured by the radar with the ones computed from 2D-video-disdrometer assuming the Pruppacher - Pitter shapes of raindrops. It was found that specific differential phase measured by the radar is somewhat smaller on average than K_{DP} estimated from the disdrometer. The reasons for such a discrepancy are analyzed.

Session 11B, Quantitative Rainfall—Multi-Parameter Approaches II (Parallel with Session 11A)

**Monday, 23 July 2001, 4:00 PM-6:00 PM**** Previous paper Next paper
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