An extraordinary extreme heavy rainfall event during 19-22 July 2021("21.7"EHRE)attacked Henan Province of North China Plain(NCP)and led to tremendous catastrophes due to the record-breaking rain-fall.Previous studies mainly focus on the individual case study of the"21.7"EHRE,which cannot give a general view of circulation characteristic from the climatic perspective,particularly for the extraordinary precipitation ex-tremes with a rare occurrence.Based on 12-hourly observed precipitation data from rain gauge stations during 1960-2021 from CMA(China Meteorological Administration)and NCEP/NCAR reanalysis data,this study in-vestigated the typical synoptic patterns responsible for the summer regional extreme precipitation events(REPEs)over NCP during 1960-2021 via the spectral clustering method and systematically revealed how the"21.7"EHRE occurred.Results show that the"21.7"EHRE occurred under a rare synoptic pattern featured by a distant typhoon over western Pacific accompanied by the farther northwestward extended western Pacific subtropic high(WPSH)and northeastward extended South Asia high(SAH).This synoptic pattern only contributes 5.97％of the total summer REPE occurrences over NCP but can lead to much stronger precipitation extremes.The water va-por transported by the strong southeasterly winds between the Typhoon In-Fa and WPSH from the western Pacific to Henan,and the intense ascending motion caused by wind shear between lower and upper troposphere over Henan Province led to the occurrence of the"21.7"EHRE.In addition,diagnosis analysis based on quasi-geo-strophic omega equation indicates that the positive feedback on intense ascending motion and diabatic heating at lower troposphere over Henan province and surrounding areas distinguishes the"21.7"EHRE from the others under the same synoptic pattern.This study investigates the dominant large-scale synoptic pattern of the"21.7"EHRE in Henan to figure out the formation mechanism of the rarest REPEs in a climatic aspect.Findings of this study provide a novel perspective on characterizing and predicting future precipitation extremes in NCP by linking the occurrence and distribution of REPEs with the synoptic patterns.
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