What Determine the Performance of the ENSO-East Asian Winter Monsoon Relationship in CMIP6 Models?

This study evaluates the relationship between El Nino-Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) in 26 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Of particular concern is the plausible factors for the model's capability of simulating the ENSO-EAWM relationship. Results show that the model's ability of simulating the ENSO-EAWM relationship is more dependent upon the longitudinal extension of ENSO-related equatorial Pacific sea surface temperature (SST) anomalies than the amplitude of the equatorial central-eastern Pacific SST anomalies. The influence of the amplitude of ENSO on the simulation of the ENSO-EAWM relationship depends on the westward extension of ENSO-related equatorial Pacific SST anomalies. Another factor for the model's ability of simulating the ENSO-EAWM relationship is the SST anomalies in the tropical western North Pacific (WNP). A westward extension of the equatorial Pacific SST anomalies shifts the west branch of anomalous Walker circulation too far westward, which causes westward displaced anomalous ascending (descending) motion around the Philippines through modulating regional meridional vertical circulation in El Nino (La Nina) years. The weak SST anomalies in the tropical WNP lead to the failure of inducing anomalous lower-level anticyclone (cyclone) over the Philippine Sea through a Rossby wave response in El Nino (La Nina) years. The accompanying weak anomalous lower-level southwesterly (northeasterly) winds along the west flank of the anomalous anticyclone (cyclone) account for the weak ENSO-EAWM relationship.