Organized Warm-Sector Rainfall in the Coastal Region of South China in an Anticyclone Synoptic Situation: Observational Analysis

Abstract

The formation and regional difference of the organized warm-sector rainfall (OWSR) near the coast of South China in an anticyclone synoptic situation were investigated, by analyzing relevant events in recent years using high-resolution observational and reanalysis data. The results show that the anticyclone synoptic situation produces marked northerly boundary-layer winds inland, and obvious northeasterly, easterly/southwesterly and southeasterly boundary-layer winds near the coast of eastern and western Guangdong Province and Guangxi Province, respectively. Compared with the northeasterly boundary-layer winds, the southwesterly, southeasterly or easterly boundary-layer winds promote favorable environmental conditions and stronger convergence with the northerly boundary-layer winds for convection initiation. Consequently, OWSR is prone to occur near the coast of western Guangdong Province and Guangxi Province. The southeasterly boundary-layer winds tend to converge beside the mountains near the boundary between Guangxi and Guangdong provinces, promoting the formation of a stable convective line along the mountains. The convective line persists with the assistance of southwesterly upper-level winds, which encourage convective cells to propagate along the convective line, producing heavy OWSR along the mountains near the boundary between Guangxi and Guangdong provinces. In contrast, a west–east convective line tends to form and maintain near the coast of Yangjiang, owing to stable convergence between the easterly (or southwesterly) and northerly boundary-layer winds reinforced by the mountains near Yangjiang. Furthermore, the coupling of westerly upper-level winds with the easterly (southwesterly) boundary-layer winds facilitates an expansion (eastward propagation) of the convective line, causing west–east-oriented heavy OWSR near the coast of Yangjiang.