Biases and improvements of the ENSO-East Asian winter monsoon teleconnection in CMIP5 and CMIP6 models

The influence of El Nino-Southern Oscillation (ENSO) on the East Asian winter monsoon (EAWM) is investigated based on the outputs of phase 6 of the Coupled Model Intercomparison Project (CMIP6) models and compared to that in phase 5 (CMIP5). Results show that overall the CMIP6 models reproduce the ENSO-EAWM teleconnection more realistically than the CMIP5 models, although they still somewhat underestimate the ENSO-EAWM teleconnection than observed. Based on the intermodel spread of ENSO-EAWM teleconnection simulated in the CMIP5/CMIP6 models, we reveal that the commonly underestimated ENSO-EAWM teleconnection among the models can be traced back to the excessive extension of the cold tongue to the equatorial western Pacific. A model with a stronger climatological cold tongue favors generating a more westward extension of the ENSO-related SST anomaly pattern, which in turn forces an anomalous cyclonic circulation over the Northwest Pacific (NWP). It offsets the anticyclonic anomalies in the NWP and weakens the ENSO-EAWM teleconnection. Compared with the CMIP5 models, most CMIP6 models better simulate SST mean state and the resultant ENSO-EAWM teleconnection. The present results suggest that substantial efforts should be made to reduce the bias in the mean-state SST for further improving the simulation and projection of the East Asian-western Pacific winter climate.

Automated summary

The influence of El Nino-Southern Oscillation (ENSO) on the East Asian winter monsoon (EAWM) is investigated using CMIP6 models and compared to CMIP5 models. The results show that CMIP6 models more accurately reproduce the ENSO-EAWM teleconnection, although it is still somewhat underestimated compared to observations. The underestimation among the models can be attributed to the excessive extension of the cold tongue to the equatorial western Pacific. Most CMIP6 models better simulate the ENSO-EAWM teleconnection compared to CMIP5 models. Efforts should be made to reduce the bias in the mean-state sea surface temperature for better simulation and projection of the East Asian-western Pacific winter climate.