The modulation of Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation on winter Eurasian cold anomaly via the Ural blocking change

Observations reveal distinct interdecadal winter Eurasian cold anomaly (ECA) centered over central Eurasia (40°–60° N, 60°–120° E), 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 decadal change from 1965–1976 to 2002–2013 using reanalysis data. It is found that the 1965–1976 winter ECA is associated with a 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⁻. UB mainly related to positive North Atlantic Oscillation is relatively short-lived and rapidly retrograde during both IPO⁺ and AMO⁻, but long-lived and shows different longitudinal movements and positions during IPO⁻ and AMO⁺. During IPO⁻, UB grows rapidly and decays slowly due to weak westerly winds and small meridional potential vorticity gradient (PV_y) over North Atlantic mid-high latitudes and Eurasian high latitudes, and moves slowly westward during its decay stage, causing strong cold anomalies over central Eurasia and its upstream region (30°–50° N, 30°–70° E). AMO⁻ has a similar effect due to the slow decay of retrograde UB. However, during AMO⁺ UB grows slowly, decays rapidly and shows eastward movement due to strong (weak) westerly winds and large (small) PV_y over North Atlantic (Eurasian) high latitudes, causing strong cold anomalies over central Eurasia and its downstream side. Through these UB-induced sub-seasonal changes, the interdecadal IPO⁻, AMO⁻ and AMO⁺ help explain the decadal variation of the winter-mean ECA from 1965–1976 to 2002–2013.