Suggested Modifications for the S-Band Polarimetric Radar Rainfall Estimation Algorithm

Abstract Utilization of specific differential phase K DP combined with specific attenuation A for rainfall estimation introduced a decade ago was a real game changer in radar quantitative precipitation estimation (QPE) at S band. The R ( A )/ R ( K DP ) QPE algorithm (named Q3DP) operationally implemented on the Multi-Radar Multi-Sensor (MRMS) system platform in the United States demonstrated well-documented improvement in rainfall estimation for the nationwide network of the WSR-88D radars, particularly for heavy rain associated with flash floods. Further modifications of R ( A ) and R ( K DP ) methodologies comprising the Q3DP algorithm are suggested in this study. A new scheme for estimating a key parameter of R ( A ) technique, the ratio α = A / K DP , is suggested that automatically takes into account its spatial variability across the radar field of view as well as inherent dependence of A on temperature. A novel approach for the use of K DP to quantify heavy rain is introduced which implies optimization of a multiplier in the power-law R ( K DP ) relation based on the combination of K DP and radar reflectivity Z . The improvement in rainfall estimation resulting from utilization of a new R ( A )/ R ( K DP ) methodology is illustrated for a few heavy rainfall events. Significance Statement The importance of accurate radar rainfall estimation is hard to overestimate. In this study, further modifications of the advanced polarimetric radar QPE methodologies are suggested to improve their performance, particularly in heavy or extreme rain. In addition to the QPE benefits, better estimates of specific attenuation will provide important advantages for radar signal attenuation correction and microphysical retrievals in rain.