The Large‐Scale Circulation Patterns Responsible for Extreme Precipitation Over the North China Plain in Midsummer

Abstract

AbstractExtreme precipitation events over the North China Plain (NCP) in midsummer during 1979–2016 are classified into two types using objective cluster analysis: a northern pattern with heavy precipitation and a central–southern pattern with relatively moderate precipitation. The large‐scale circulation patterns responsible for the midsummer extreme precipitation are then determined. In the northern NCP type, extreme precipitation accompanies a zonal gradient between an anomalous low‐pressure system at high latitudes and the westward‐ and northward‐extended western North Pacific subtropical high (WNPSH). Anomalous southwesterlies flow is driven by a trough that extended from the high latitudes to the northern NCP, where it encounters southeasterly wind flow induced by an anomalously northward‐extended WNPSH and a southern low‐pressure anomaly at low latitudes. Anomalous amounts of moisture are mainly transported from the tropical western Pacific by southeasterlies. In the central–southern NCP type, remarkable anomalous low‐pressure systems control all of northern China with centers over the Sichuan Basin and northeast China. The westward‐extended WNPSH occupies further south than that of the northern NCP type. The southwesterly low‐level jet (LLJ) is more prevalent in the central–southern NCP type than in the northern NCP type. This southwesterly LLJ plays an important role in extreme precipitation over the central–southern NCP by transporting moisture primarily from the Bay of Bengal and the South China Sea and generating convergence. In addition, the upper‐level anomalous strong divergence that is anchored over the right entrance of the westerly jet makes a greater contribution to extreme precipitation in the northern type than in the central–southern type.