The East Asian Winter Monsoon and its Relationship with El Niño–Southern Oscillation: Present and Future

Using a reanalysis dataset and Coupled Model Intercomparison Project Phase 6 (CMIP6) models, this study investigated the southern and northern modes of the East Asian winter monsoon (EAWM) and their relationship with El Niño–Southern Oscillation (ENSO). The EAWM northern mode (EAWM_N) showed a steady and strong connection to the circulation in the middle and high latitudes throughout the period of 1979–2013, resembling the Eurasian pattern. The positive phase of the Eurasian pattern enhanced the sea-land pressure gradient in the middle latitudes of East Asia and strengthened northerly winds flowing from high latitudes to South China, resulting in a strong EAWM_N. The relationship between the EAWM_N and ENSO changed from insignificant to significant in the late 1990s, which correlated the transition of Walker circulation from east to west. In contrast, the EAWM southern mode (EAWM_S) was closely related to an anomalous cyclone over the Philippine Sea and exhibited a stable and robust inverse correlation with ENSO. Projections from 12 CMIP6 models indicate that the unstable negative correlation of EAWM_N with ENSO will be intensified, while the strong link between EAWM_S and ENSO will remain stable in the future under both the SSP1-2.6 and SSP5-8.5 scenarios. Increased variability in future Niño 3.4 with external forcing corresponds to increases in the variability of EAWM_S. These findings suggest that future research into the northern and southern modes of the EAWM would be beneficial as the climate continues to warm.