The Modulation of Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation on winter Eurasian Cold Anomaly via the Ural Blocking Change

Observations revealed distinct interdecadal winter Eurasian cold anomaly (ECA) centered over central Eurasia (40o-60oN,60o-120oE), with a more southwestward extension during 1965-1976 than during 2002-2013. In this paper, Ural blockings (UB) in association with the Interdecadal Pacific Oscillation (IPO) and Atlantic Multi-decadal Oscillation (AMO) are analyzed to explain the ECA’s interdecadal change using reanalysis data. It is found that the 1965-1976 winter ECA is associated with the negative-phase IPO (IPO-) together with negative-phase AMO (AMO-), while the 2002-2013 ECA is related to positive-phase AMO (AMO+) concurring with IPO-. The UB mainly related to positive North Atlantic Oscillation is long-lived during IPO- and AMO+ and shows different longitudinal position and movement, but short-lived and retrograde during both IPO+ and AMO-. During IPO-, the UB grows rapidly and decays slowly due to weak westerly winds and small meridional potential vorticity gradient (PVy) over North Atlantic mid-high latitudes, and moves westward mainly during its decay stage, causing strong cold anomalies over central Eurasia and its upstream region (30o-50oN, 30o-70oE). Such a slow blocking decay is also seen during AMO-. However, during AMO+ the UB grows slowly, decays rapidly and shows eastward movement due to strong westerly winds and large PVy over North Atlantic high latitudes, causing strong cold anomalies over central Eurasia and its downstream region (30o-50oN, 90o-130oE). Through these UB-induced sub-seasonal changes, the interdecadal IPO-, AMO- and AMO+ help explain the variation of the winter-mean ECA from 1965-1976 to 2002-2013.