Mitigating Spatial Discontinuity of Multi-Radar QPE Based on GPM/KuPR

The reflectivity factor bias caused by radar calibration errors would influence the Quantitative Precipitation Estimation (QPE) relations and induce estimation errors, which result in spatial discontinuity in Multiple Ground Radars QPE (MGR-QPE) products. Due to the sampling differences and methodological random errors, the associated discontinuity cannot be thoroughly solved by the single-radar calibration methods. Thus, a multiple-radar synchronous calibration method was proposed to mitigate the spatial discontinuity of MGR-QPE. Firstly, the spatial discontinuity was solved by the inter-calibration of adjacent ground radars, then calibration errors were reduced by referring to the Ku-Band Precipitation Radar (KuPR) carried by Global Precipitation Measurement (GPM) Core Observatory as a standard reference, and finally, Mosaic Reflectivity and MGR-QPE products with spatial continuity were obtained. With the three S-band operational radars covering the lower reaches of the Yangtze River in China, the new method was evaluated using the data of four representative precipitation events. It was found 1) the spatial continuity of the reflectivity factor and precipitation estimation field was significantly improved after correction, and the reflectivity difference between adjacent radars were reduced by 78% and 82%, respectively. 2) The accuracy of MGR-QPE was also increased, and the normalized absolute error was reduced by 0.05 - 0.12, and the QPE values were closer to the gauge-observed data.