Interdecadal Variation of the Warm Arctic–Cold Eurasia Mode and Its Association with North Atlantic Sea Surface Temperature

Based on the surface air temperature datasets from NASA (National Aeronautics and Space Administration)’s Goddard Institute for Space Studies, 20th century’ s reanalysis data from National Oceanic and Atmospheric Administration–Cooperative Institute for Research in Environmental Sciences, and the historical experiments of the Coupled Model Intercomparison Project Phase 6, this study analyzes the interdecadal variation characteristics of the Warm Arctic–Cold Eurasia (WACE) mode in the Eurasia and Arctic region from 1910/1911 to 2019/2020 during the boreal winter after removal of external forcing. The results show that the WACE displays remarkable interdecadal variability. When WACE is in the interdecadal positive phase, the high-frequency Ural block favors heat transport to the polar regions, leading to warm advection and water vapor transport. This, in turn, causes water vapor convergence in the polar region, leading to an increase in downward long-wave radiation and an increase in convective activity and latent heat release. This results in increasing temperatures in this region. At the same time, the weakening of the polar vortex and westerly winds in Eurasia and the high-frequency of Ural blockage favor cold air advection into Eurasia. Divergence of water vapor in Eurasia reduces downward long-wave radiation, leading to decreased convective activity and latent heat release, which in turn decreases the temperatures in Eurasia. The authors used the CAM3.0 atmospheric circulation model to simulate the North Atlantic SST (Sea Surface Temperature) influence on WACE. Model results are consistent with the statistical results, further illustrating that the North Atlantic SST positive anomaly can force the lower and upper atmospheric circulation anomalies, leading to water vapor convergence in the polar regions and divergence in Eurasia, thus affecting decadal variability of WACE.