North Atlantic origin of interdecadal variability of WACE pattern

Abstract

We investigate the origin of the interdecadal variability in the Warm Arctic and Cold Eurasia (WACE) pattern, which is defined as the second empirical orthogonal function of surface air temperature (SAT) variability over Eurasian continent in winter. By analyzing the Twentieth Century Reanalysis dataset, we found that the WACE pattern has experienced a seemingly periodic interdecadal variation over the twentieth century. This long-term variation in the Eurasian SAT is attributable to the altered coupling between the Siberian High and intraseasonal Rossby wave emanating from the North Atlantic. It is further identified that these atmospheric circulation changes in Eurasia is largely controlled by the decadal amplitude modulation of the climatological stationary waves over the North Atlantic region. The altered decadal mean condition of stationary wave components brings changes in local baroclinicity and storm track activity over the North Atlantic, which jointly change the intraseasonal Rossby wave generation and propagation characteristics as well. With simple stationary wave model experiments, we confirm how the altered mean flow condition in North Atlantic acts as a source for the growth of the Rossby wave that leads to the change in the downstream WACE pattern. It would be worthwhile for a better understanding of the current climate in the earth climate system as well as estimating upcoming changes.