Simultaneous measurements of heavy rain using S-band and C-band polarimetric radars

Rainfall estimation using S-band and C-band polarimetric radars has been regularly performed in central Oklahoma during the system and operational tests of the pre-prototype of the operational polarimetric WSR-88D radar (KOUN). The results of S-band measurements of rainfall by the KOUN radar are compared with results of simultaneous observations using C-band dual-polarization radar (OU PRIME) belonging to the University of Oklahoma. These closely located radars operated continuously and large sets of simultaneously collected data have been obtained. The focus was on polarimetric QPE analysis in heavy rain where C-band radar measurements can be compromised by strong impact of attenuation and resonance scattering. Radar rainfall estimates are validated using dense networks of micronet and mesonet gages. The Oklahoma City Micronet was particularly useful to test the performance of different QPE algorithms during two extreme flash floods events in the OKC metro area associated with heavy tropical rain. It is shown that the algorithms utilizing specific differential phase KDP for heavier rain and radar reflectivity Z (after correction attenuation) for lighter rain perform better than the conventional R(Z) relations but tend to underestimate tropical rain at S and C bands if “climatological” rainfall relations optimized for Oklahoma are utilized. Negative bias is eliminated at S band if the combinations of KDP and ZDR for heavier rain and Z and ZDR for lighter rain are used but similar approach may not work at C band due to residual errors in differential attenuation correction and lower values of cross-correlation coefficient.