CMIP6模式对西北太平洋异常反气旋的模拟偏差:主要模态及其来源分析OA

The western North Pacific anomalous anticyclone(WNPAC)is a key atmospheric circulation system linking El Niño-Southern Oscillation(ENSO)events to climate variability in East Asia.During El Niño winters,anomalous warming in the equatorial central-eastern Pacific induces a Gill-type response that generates an anoma-lous anticyclone over the western North Pacific,exerting far-reaching influences on the East Asian monsoon,win-ter temperature,and precipitation patterns.Despite its importance,the ability of state-of-the-art climate models to accurately simulate the WNPAC remains insufficiently understood. This study provides a systematic assessment of 25 models participating in the Coupled Model Intercomparison Project Phase 6(CMIP6)in simulating the climatological WNPAC during the historical period(1940-2014)and further investigates the physical origins of model biases.The results show that the multi-model mean(MMM)significantly underestimates the strength of the WNPAC and shifts its center westward relative to observations.While observations place the anticyclonic center over the Philippine Sea,the CMIP6 MMM locates it over the South China Sea with a substantially weakened amplitude.This systematic bias suggests that CMIP6 mod-els tend to underestimate ENSO teleconnections affecting the East Asian winter climate. To examine intermodel diversity,empirical orthogonal function(EOF)analysis is applied to the WNPAC in both CMIP6 models and observations.Two leading modes are identified.EOF1(40.6%of variance explained)re-presents zonal displacement of the WNPAC,distinguishing models with westward-versus eastward-shifted anticy-clones.Most models exhibit positive principal component(PC1)values relative to observations,indicating a sys-tematic westward bias.EOF2(25.2%of variance explained)characterizes variations in WNPAC intensity,with most models underestimating its strength. Regression analyses based on the principal components reveal the physical mechanisms underlying these bia-ses.The zonal displacement bias(EOF1-type)is strongly associated with the westward extension of El Niño-in-duced SST anomalies in the central Pacific.Models with stronger equatorial cold tongue biases exhibit enhanced zonal SST gradients and stronger nonlinear zonal advective feedbacks,which shift anomalous convection and the associated Rossby wave response westward.This indicates that an unrealistic mean-state cold tongue is a primary driver of the systematic westward bias of the WNPAC in CMIP6 models. The intensity bias(EOF2-type)is linked to variations in the strength of the Bjerknes"wind-SST"positive feedback.Models with stronger air-sea coupling simulate greater weakening of the trade winds during El Niño,leading to enhanced SST cooling in the western Pacific and a stronger WNPAC response.The PC2 values show a significant correlation(r=0.65)with independently diagnosed wind-SST feedback strength,confirming that un-derestimated air-sea coupling in most CMIP6 models contributes to the widespread weak WNPAC bias. Finally,a skill score is constructed based on the distance between each model's(PC1,PC2)pair and the observed reference point,weighted by the explained variance.The best-performing models(KIOST-ESM,BCC-ESM1,CAMS-CSM1-0,MPI-ESM1-2-LR,and EC-Earth-Veg)successfully reproduce the location and intensity of the WNPAC,whereas models such as NESM3,CMCC-CM2-SR5,TaiESM,FIO-ESM-2-0,and NorCPM1 ex-hibit the poorest performance. Overall,this study demonstrates that systematic biases in CMIP6 models—particularly an overly strong equa-torial cold tongue and a weakened wind-SST coupling—jointly lead to a westward-shifted and weakened WNPAC response to El Niño.These findings highlight the uncertainties in simulating ENSO-WNPAC-East Asia teleconnec-tion under future climate change.