Typical circulation patterns and associated mechanisms for persistent heavy rainfall events over Yangtze–Huai River Valley during 1981–2020

The persistent heavy rainfall events (PHREs) over Yangtze–Huai River Valley (YHRV) during 1981–2020 are chosen and classified into three types (type-A, type-B and type-C) according to pattern correlation. The anomalous cyclonic disturbance over the southern part of the YHRV during type-A events is primarily maintained by the propagation of Rossby wave energy originating from the northeast Atlantic in the mid–upper troposphere and the northward propagation of Rossby wave packets from the western Pacific in the mid–lower troposphere. The zonal and the northward propagation of Rossby wave packets during type-B events is stronger than that for type-A events, which induces eastward propagation of stronger anomaly centers of geopotential height from the northeast Atlantic Ocean to the YHRV and a meridional anomalous feature of geopotential height over the Asian continent. Type-C events have ‘two ridges and one trough’ in the high latitudes of the Eurasian continent, but the anomalous intensity of the western Pacific subtropical high (WPSH) and the trough of the YHRV region are weaker than those for type-A and type-B events. The composite synoptic circulation of four PHREs in 2020 is basically consistent with that of the corresponding PHRE type. The location of the South Asian high (SAH) in three of the PHREs in 2020 moves eastward as in the composite of the three types, but the position of the WPSH of the four PHREs is obviously westward and northward. Two water vapor and two cold air pathways are tracked during the four PHREs in 2020.