Resolve the Decadal Variation in the Relationship Between ENSO and East Asian Winter Monsoon

The relationship between the El Niño–Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) shows pronounced decadal variability, and the modulation of the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) remain highly controversial. In this study, reanalysis data for 1951–2020 are used to re-examine the decadal modulation of the ENSO–EAWM relationship. A running-correlation decomposition is applied to identify the key source of nonstationarity, and a multiple regression framework is further used to quantify the respective contributions of the AMO, PDO, and their nonlinear interactions with ENSO. Results indicate that the decadal variations in the ENSO–EAWM relationship are mainly controlled by changes in their covariance rather than by variations in ENSO or monsoon amplitude. The AMO and PDO are found to modulate the relationship through distinct regional pathways: the AMO primarily affects the EAWM over central and South China, whereas the PDO exerts a strong influence over South China. These regionally dependent modulations help reconcile previous conflicting results and provide a more unified interpretation of the decadal variability of ENSO impacts over East Asia.