In Situ Observations of Rain Rate and Precipitation Microphysics over the Coastal Area of South China: Perspectives for Satellite Validation

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Abstract This study investigates precipitation observed by a set of collocated ground-based instruments in Zhuhai, a coastal city located at the southern tip of the Pearl River Delta of Guangdong Province in South China. Seven months of ground-based observations from a tipping-bucket rain gauge (RG), two laser disdrometers (PARSIVEL and Present Weather Sensor 100 (PWS)], and a vertically pointing Doppler Micro Rain Radar-2 (MRR), spanning from December 2021 to July 2022, are statistically evaluated to provide a reliable reference for China’s spaceborne precipitation measurement mission. Rainfall measurement discrepancies are found between the instruments though the collocated deployment mitigates uncertainties originating from spatial/temporal variabilities of precipitation. The RG underestimates hourly rain amounts at the observation site, opposite to previous studies, leading to a percent bias (Pbias) of 18.2% of hourly rain amounts when compared to the PARSIVEL. With the same measurement principle, the hourly accumulated rain between the two laser disdrometers has a Pbias of 15.3%. Discrepancies between MRR and disdrometers are assumed to be due to different temporal/spatial resolution, instrument sensitivities, and observation geometry, with a Pbias of mass-weighted mean diameter and normalized intercept parameter of gamma size distribution less than 9%. The vertical profiles of drop size distribution (DSD) derived from the MRR are further examined during extreme rainfalls in the East Asian monsoon season (May, June, and July). Attributed to the abundant moisture which favors the growth of raindrops, coalescence is identified as the predominant effective process, and the raindrop mass-weighted mean diameter increases by 33.7% when falling from 2000 to 600 m during the extreme precipitation event in May. Significance Statement The performance and reliability of ground-based observations during precipitation scenarios are evaluated over the coastal area of South China, in preparation for China’s spaceborne precipitation measurement mission. A comparison study, which is carried out to assess the accuracy of rainfall and drop size distribution (DSD), demonstrates that the observation results are relatively reliable though discrepancies between the instruments still exist, while the accompanying microphysical process during extreme precipitation can be quantified with profiling capabilities at the observatory. An accurate and reliable rainfall characterization over the coastal region in South China can contribute to the validation of satellite rainfall products and provide further insights into the microphysical parameterization schemes during extreme precipitation.

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