Inter-Model Spread of the Simulated Winter Surface Air Temperature Over the Eurasian Continent and the Physical Linkage to the Jet Streams From the CMIP6 Models

The model uncertainty, one of the major sources of projection uncertainty, is still a challenge in the climate simulation. In this study, we investigated the inter-model spread of the simulated winter surface air temperature (SAT) over the Eurasian continent and the physical link to the upper-level jet streams from the Coupled Model Inter-comparison Project Phase 6 models. Extracted by the inter-model empirical orthogonal function analysis, the leading inter-model spread of SAT over the Eurasian continent is characterized by a cold pattern, particularly over high latitudes, which is closely associated with the out-of-phase variation in the intensity of the East Asian polar front jet (EAPJ) and East Asian subtropical jet (EASJ). The weakened-EAPJ-enhanced-EASJ pattern is linked to the intensified Siberian high, the strengthened Aleutian low, and the deepened East Asian trough. All the variations would benefit the cold air invasion, resulting in the leading inter-model spread of the SAT. The possible mechanism for the inter-model uncertainty in the out-of-phase variation in the intensity of the two jets would be traced to the cooling over the Northwest Pacific oceans, which has reduced (enhanced) the meridional temperature gradient over high (low) latitudes and thereby contributed to the out of phase variation in the two jets. Our findings would help provide a potential metric for understanding the winter SAT change over the Eurasian continent. Plain Language Summary The winter surface air temperature (SAT) over the Eurasian continent has profound economic and social impacts, however, there are large uncertainties in the climate model simulations. In this study, the inter-model spread is utilized to derive the inter-model uncertainty in the winter SAT over the Eurasian continent. The leading mode is a cold pattern over the Eurasian continent, which is closely related to the out-of-phase concurrent variation in the intensity of the upper-level jet streams, resulting in the strengthened East Asian Winter monsoon. With an emphasis on the physical link between the East Asian jet streams and the winter SAT over the Eurasian continent, our findings provide a perspective of physical linkage to understand the traces of model uncertainty.