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

Binhe Luo,Ian Simmonds,Aiguo Dai,Lixin Wu,Dehai Luo

doi:10.1007/s00382-021-06119-7

Abstract

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 (PVy) 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) PVy 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.

Highlights

Earth’s warming rate slowed down noticeably during 2000-2013, which is often referred to as the recent global warming hiatus (Kaufmann et al 2011; Karl et al 2015)
Atlantic Multidecadal Oscillation (AMO)+ or AMO- cannot produce strong cold anomaly over central Eurasia south of 60oN as seen in observations (Fig. 1b-c) if the Ural blocking (UB) is absent, Interdecadal Pacific Oscillation (IPO)- without UB cannot contribute to the interdecadal cold anomalies over central Eurasia (Fig.5b). These results suggest that UB events modulated by IPO, AMO- and AMO+ play an important role in the winter cold anomaly over central Eurasia
We first examined the dependence of winter Ural blocking (UB) and its impact on Eurasian surface air temperature (SAT) on the phase of IPO and AMO as defined by

Summary

Introduction

Earth’s warming rate slowed down noticeably during 2000-2013, which is often referred to as the recent global warming hiatus (Kaufmann et al 2011; Karl et al 2015). Eurasia and its upstream side during the UB events for IPO- (Fig. 6a) as the UB has a strong negative height anomaly at 60oE and its east side, a long duration of about 9.5 days with rapid growth and persistent slow decay, and a small westward speed of about -0.2 m/s in the Ural region mainly occurring after lag 3 (Fig. 7d).

Results

Conclusion