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 respective relationships with the El Niño-Southern Oscillation (ENSO). The EAWM northern mode (EAWM_N) exhibited a consistent and strong connection with the mid- and high-latitude atmospheric circulation during 1979-2013, resembling the Eurasian tele-connection pattern. The positive phase of this pattern enhanced the sea-land pressure gradient across the mid-latitude 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 shifted from insignificant to significant in the late 1990s, coinciding with a westward transition of the Walker circulation. In contrast, the EAWM southern mode (EAWM_S) was closely associated with an anomalous cyclone over the Philippine Sea and exhibited a stable, robust inverse correlation with ENSO. Projections from 12 CMIP6 models indicated that the unstable negative correlation of EAWM_N with ENSO would intensify, while the robust linkage between EAWM_S and ENSO was expected to persist under both the SSP1-2.6 and SSP5-8.5 scenarios. Additionally, increased future variability in the Niño 3.4 index, driven by external forcing, corresponded well to enhanced variability of EAWM_S. These findings underscore the necessity for further research into the distinct behaviors of the northern and southern EAWM modes under the background of ongoing climate warming. [ABSTRACT FROM AUTHOR]