Characteristics and Causes of“21.7” Extreme Rainstorm in Northern Henan Province

The extreme heavy rainfall in northern Henan province from July 17 to 22 2021 was analyzed by using the sounding surface automatic station Doppler radar and ERA5. The results show that the extreme heavy rainfall process is characterized by long duration of heavy rainfall, extreme precipitation intensity and obvious topographic influence. The extreme rainstorm occurred under stable Synoptic scale meteorology conditions, with the westward extension of the Japan Sea High and the Northwest Passage of Typhoon Chapaka (No. 2107) against the background of Typhoon Fireworks (No. 2106) , the strengthening of the southward jet of the southward southeast jet in the periphery of the yellow quasi-vortex provides abnormally sufficient water vapor and energy conditions for the occurrence of heavy precipitation, the strong dynamic convergence and uplift of the warm and humid advection forcing, the superimposed topographic effect and the southward diffusion of the low-level weak cold air in the middle and lower troposphere are the important conditions for the formation of strong precipitation, the transformation of the convective instability stratification characteristics of“Strong-weak-strong-weak” indicates that there are two complementary physical mechanisms in the process of heavy precipitation. The convective systems of extreme short-term heavy precipitation (hourly precipitation > 50 mm) in different stages have different morphological structure and evolution characteristics. However, from the vertical distribution of radar echoes, the convective systems all have the characteristics of“Low centroid”, the centroid strength is more than 55 dB and the strong echo of more than 50 B extends vertically to more than 58 m in duration 1. The backward development of the heavy rainfall convective system over the first 30 m of Taihang Mountains is obvious. On the one hand, it is related to the southerly extension of the topographic convergence line formed by the westerly easterly and northeasterly winds, on the other hand, it is also related to the strong precipitation cold pool effect, which impels the northward wind to develop southward.