Abstract:
The extreme characteristics of the “21.7” rainstorm that occurred in Henan Province during July 19–21, 2021, including the impact range, duration, rainfall intensity, and cumulative precipitation, were studied using national precipitation data. With ERA5 reanalysis data and generalized Omega equation, key physical factors affecting vertical movement were studied, and their differences from the “75.8” rainstorm (torrential rainstrom in Henan Province in August 1975) were discussed. The results show that about 10% of the stations in Henan Province accumulated precipitation exceeding 500 mm during the “21.7” rainstorm, with an average precipitation of 92.8 mm on July 20, 2021, ranking first since 1961. On that day, the hourly precipitation during 1600 BJT–1700 BJT (Beijing time) in Zhengzhou broke the extreme hourly record in the Chinese Mainland (201.9 mm). Both rainstorms were accompanied by the transport of water vapor from typhoon flows. The water vapor of the “21.7” rainstorm primarily originated from the vapor transport of the southeastern jet stream between Typhoon Fireworks and the sub-high, while the “75.8” rainstorm had two water vapor channels, namely, the southwest airflow from the Indian Ocean and the southeast airflow from the western Pacific Ocean. In both rainstorms, the total
Q-vector divergence anomalies of the generalized Omega equation were related to areas of strong vertical movements. The vertical velocity intensity and total
Q-vector divergence intensity of the “21.7” rainstorm were slightly weaker than those of the “75.8” rainstorm. The vertical motion of the “21.7” rainstorm primarily resulted from the combined low-level dynamics and thermal forcing, whereas that of the “75.8” rainstorm mainly resulted from the middle–low-level thermal forcing and low-level dynamic forcing. The different spatial distributions of vertical motion may be one of the reasons that the Zhengzhou area is prone to short-duration intense precipitation with low centroids and high efficiency.