Simulation of polarimetric radar variables in rain at S-, C- and X-band wavelengths

Abstract. Polarimetric radar variables of rainfall events, like differential reflectivity Z_DR, or specific differential phase K_DP, are better suited for estimating rain rate R than just the reflectivity factor for horizontally polarized waves, Z_H. A variety of physical and empirical approaches exist to estimate the rain rate from polarimetric radar observables. The relationships vary over a wide range with the location and the weather conditions. In this study, the polarimetric radar variables were simulated for S-, C- and X-band wavelengths in order to establish radar rainfall estimators for the alpine region of the form R(K_DP), R(Z_H, Z_DR), and R(K_DP), Z_DR. For the simulation drop size distributions of hundreds of 1-minute-rain episodes were obtained from 2D-Video-Distrometer measurements in the mountains of Styria, Austria. The sensitivity of the polarimetric variables to temperature is investigated, as well as the influence of different rain drop shape models – including recently published ones – on radar rainfall estimators. Finally it is shown how the polarimetric radar variables change with the elevation angle of the radar antenna.