资源环境科技发展态势分析平台

This study investigates the large-scale atmospheric processes that lead to U.S. precipitation variability in late summer to midfall (August-October; ASO) and shows that the well-recognized relationship between North Atlantic Subtropical High and U.S. precipitation in peak summer (June-August) significantly weakens in ASO. The working hypothesis derived from our analysis is that in ASO convective activity in the Caribbean Sea, modulated by the tropical Pacific-Atlantic sea surface temperature (SST) anomaly contrast, directly influences the North American Low-Level Jet and thus U.S. precipitation east of the Rockies, through a Gill-type response. This hypothesis derived from observations is strongly supported by a long-term climate model simulation and by a linear baroclinic atmospheric model with prescribed diabatic forcings in the Caribbean Sea. This study integrates key findings from previous studies and advances a consistent physical rationale that links the Pacific-Atlantic SST anomaly contrast, Caribbean Sea convective activity, and U.S. rainfall in ASO.