Long-Term Assessment of the Reflectivity Biases and Wet-Radome Effect Using Collocated Operational S- and C-band Dual-Polarization Radars

This study assessed the long-term radar reflectivity (Z) biases of collocated S- (RCWF) and C-band dual-polarization radars (RCMD), operated by the Central Weather Bureau (CWB) of Taiwan (121.77 °E, 25.07 °N). The systematic bias, wet-radome effect (WRE), and attenuation effect were investigated. The algorithm of self-consistency utilizes Z, differential reflectivity (Z_dr), and a specific differential phase (K_dp) to estimate the systematic bias and WRE of both radars. Eleven years of disdrometer data in northern Taiwan were used to obtain the self-consistency and K_dp-based attenuation correction relation coefficients. Subsequently, a series of sensitivity tests were conducted to examine the influence of these coefficients on bias and attenuation corrections. The K_dp(Z,Z_dr) relationship outperformed that of K_dp(Z). The K_dp(Z,Z_dr) relationship with seasonal coefficients and systematic bias-corrected Z_dr constituted the optimal procedure. The corrected Z of collocated radars was in good agreement, lending further validity to the correction schemes. The results demonstrated that the stable systematic bias values of RCWF and RCMD were −1.89 to −1.14 dB and −2.46 to −1.87 dB, respectively. During the WRE period, additional underestimations of Z by nearly 4 and 7 dB were recorded for RCWF and RCMD, respectively. The mean value of radar reflectivity near radar (Z_nr) was obtained to identify the WRE period. In this study, an innovative quadratic polynomial fitting equation was proposed to investigate the systematic and WRE biases using Z_nr. Moreover, a pronounced wind intensity dependency of the WRE could be observed in the quadratic polynomial fitting equation.

Keywords: radar data quality; wet-radome effect; attenuation; self-consistency