Using multiple reanalysis datasets, this study reveals that the variability in the Western Paci c pattern (WP) in boreal winter has shown notable changes during recent decades. The variability in the winter WP exhibited a marked weakening trend before the early 2000s and increased slightly thereafter. Two epochs with the highest and lowest WP variabilities are selected for a comparative analysis. Winter WP-related meridional dipole atmospheric anomalies over the North Paci c were stronger and had a broader range during the high-variability epoch than during the low-variability epoch. Correspondingly, the winter WP had larger impacts on surface temperature variations over Eurasia and North America during the highvariability epoch than during the low-variability epoch. We nd that the shift in the winter WP variability is closely related to changes in the connection between the winter WP and the El Niño-Southern Oscillation (ENSO) and to changes in the amplitude of the North Paci c storm track. Speci cally, ENSO had a closer connection with the WP during the high-variability epoch, at which time the amplitude of the North Paci c storm track was also stronger. During the high-variability epoch, the extratropical atmospheric anomalies generated by the tropical ENSO shifted westward and projected more on the WP-related atmospheric anomalies, thus contributing to an increase in WP variability. In addition, the larger amplitude of the North Paci c storm track that occurred during the high-variability epoch led to the stronger feedback of synoptic-scale eddies to the mean ow and contributed to stronger WP variability. Further analysis indicates that the change in the connection of ENSO with the WP may be partly related to the zonal shift of the sea surface temperature anomaly in the tropical Paci c associated with ENSO.

The western Pacific pattern (WP) is one of the most important atmospheric teleconnections over the Northern Hemisphere (NH) in boreal winter, which plays key roles in regulating weather and climate variations over many parts of the NH. This study evaluates ability of the coupled models participated in CMIP5 and CMIP6 in capturing the spatial pattern, dominant frequency, and associated climate anomalies of the winter WP. Ensemble means of the CMIP5 and CMIP6 models well capture spatial structures of the WP, with slightly higher skills for the CMIP6. However, the northern (southern) centre of the WP is shifted westward (eastward) relative to the observations, and the strength of the northern centre is overestimated in most CMIP5 and CMIP6 models. CMIP6 shows an improvement in simulating the dominant periodicity of the WP. WP-related climatic anomalies in most parts of the NH can be well simulated. However, there exists a large spread across the models in simulating surface air temperature (SAT) anomalies in Russian Far East and Northwest North America, which is attributable to the diversity of the intensity of the WP’s northern lobe. Most CMIP5 and CMIP6 models largely overestimate the WP-related precipitation anomalies over Siberia, which is partly due to the overestimation of mean precipitation there. Furthermore, most models simulate a close relation of the WP and Arctic Oscillation (AO), which does not exist in observation. The CMIP5 and CMIP6 models with weak WP-AO relations have better ability than the models with strong WP-AO relations in capturing the WP-related SAT and precipitation anomalies over the NH, especially over Eurasia.