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On 20thJuly 2021, an extreme rainfall event occurred at Zhengzhou city in China with maximum hourly rainfall of 201.9 mm and 24h accumulated rainfall of 624.1 mm at Zhengzhou weather station. From 8:00 (BJT) 17th to 8:00 (BJT) 23rd, the maximum accumulated rainfall reaches 1122.6 mm at the Hebi Science and Technology Innovation Center Weather Station.In this study, multi-source observations including dense surface observations, Doppler weather radar network, radio sounding, and wind profiler were used to analyze the evolution of the rainfall process. Quality control and data analysis methods were implemented to check and merge the individual observations.The dense observations provide an opportunity to analyze the distributions of the rainfall, the vortex, convergence zone, vertical wind share, and the interaction between the winds and mountains. Surface observations and radar retrieved winds provide a three dimensional wind field with horizontal resolution of a few kilometers and vertical resolution of five hundred meters. More details were shown by the data. For example, the vortex is not obvious in surface observations in 19th and 20th , while radar retrieved winds shown a vortex structure in higher levels. The mountains enhanced the convergence of lower level winds which are important for forming the convective storms.The nudging and the 4Dvar methods were tested to assimilate the dense observations. Based on the experiments, high resolution reanalysis data were produced using the dense observations and WRF model. More details about the heavy rainfall case will be shown in this study based on hourly observations and the reanalysis data.
Xudong Liang (Fri,) studied this question.