Rainbelt Properties of Persistent Heavy Precipitation over the Yangtze River Basin and Associated Three-dimensional Circulations

Abstract In this study, we objectively identified rain belts of persistent precipitation processes over the Yangtze River Basin during 1961–2021 based on an improved rotating calipers algorithm. Considering the accumulated precipitation volume as the flood-inducing indicator, persistent heavy precipitation events were identified and categorized into three types—along, north, and south of the Yangtze River—by applying K -means clustering for spatial similarity. Results showed that events along and in the south of Yangtze are more persistent and more flood-inducing than events in the north of Yangtze. Composite analysis revealed the relevant three-dimensional stable circulation patterns and indicated that the location of their rain belts is determined by circulation configurations. For events along the Yangtze, an eastward-propagating wave train facilitates a single-blocking high and deepens the East Asian trough. A southeastward-positioned South Asian high (SAH) and intensified westerly jet support a strong divergence in the Yangtze River Basin at 200 hPa. The western Pacific subtropical high (WPSH) stretches southwestward with a strong low-level jet, inducing warm and humid air to converge with cold air along the Yangtze. For events in the south of the Yangtze, a relatively southeastward wave train maintains under double-blocking highs. The northeast sector of the SAH, the westerly jet, WPSH, and low-level jet are located more to the south. Lastly, events in the north of the Yangtze are associated with the development of a blocking high and a dominant belt of low pressure to the south. The unfavorable circulation pattern inhibits cold air invasion, resulting in relatively weaker precipitation with shorter duration.