资源环境科技发展态势分析平台

Methods to define the East Asian monsoon usually involve ad hoc and diverse criteria. This study adopts a simple and coherent approach based on self‐organizing map to systematically derive the monsoon annual cycle based on 850‐hPa wind fields. The derived onset dates in the warm season agree well with the literature despite lacking documentations for winter‐season stages. Linear regression suggests an inverse relationship between the length of the Spring (Meiyu) stage and that of the Pre‐Meiyu (Mid‐summer) stage, suggesting predictability of the Meiyu and Fall onsets. The Aleutian Low, the western North Pacific subtropical high and the upper‐level westerlies play important roles in the Spring, Pre‐Meiyu and Meiyu onsets. Observations reveal strong rain belt events form right after the monsoonal wind onsets in the warm season. The proposed approach to deriving monsoon stages and onsets would be useful for monsoon climate studies and operational monsoon diagnosis and forecasting.