Practical Issues in X-band Radar Rainfall Estimation Over Complex Terrain

Abstract:

As part of the NOAA Advanced Quantitative Precipitation Information (AQPI) program, high-resolution gap-filling X-band polarimetric radars are being deployed over the San Francisco Bay Area to improve precipitation monitoring and forecasting. However, a number of practical issues need to be addressed in order to fully take advantage of the X-band observations in this complex terrain region, including the corrections of attenuation and partial beam blockage. This study aims to improve X-band radar rainfall mapping over complex terrain by addressing these practical issues. In particular, an improved self-consistent (ZPHI) approach for attenuation correction is developed. Compared to the conventional ZPHI method, this improved approach incorporates a non-negative constraint on the specific attenuation. In addition, the co-polar correlation coefficient is utilized to partition the differential phase profiles into independent range segments, and a minimization constraint is imposed on the difference between preprocessed and reconstructed differential phase shift. After the enhanced attenuation correction, an effective partial beam blockage (PBB) correction procedure is designed, which considers the immune characteristics of differential phase to the PBB effect. This paper also investigates the performance of specific differential phase (Kdp)-based rainfall estimation algorithms, which are commonly recommended for X-band applications since differential phase is more sensitive to rainfall at higher frequencies. Case studies during the 2019-2020 storm season are detailed, and the performance of high-resolution X-band rainfall products are demonstrated through cross-comparison with surface rain gauge measurements.