North Atlantic multidecadal footprint of the recent winter warm Arctic–cold Siberia pattern

Abstract

The multidecadal regulation of wintertime extreme cold temperatures over Eurasia by the change of the North Atlantic sea surface temperature (SST) from 1950–1983 (P1) to 1984–2017 (P2) is examined in this paper. The warm Arctic–cold Siberia (WACS) trend pattern shows a distinct interdecadal transition from P1 to P2, which has a footprint of the Atlantic Multidecadal Oscillation (AMO). The positive trend of the WACS pattern during P2 coincides with the transition of AMO from its negative phase (AMO−) to positive phase (AMO+). The sea-ice reduction in Barents–Kara Seas (BKS) owing to AMO+ contributes to the BKS warming in the WACS pattern trend, while it also reduces the meridional potential vorticity gradient (PVy) over Eurasia and increases the persistence of Ural blocking (UB), thus favoring a positive WACS trend, especially a Siberian cooling trend during P2. During P1, when the AMO changes from AMO+ to AMO−, a reversed WACS pattern trend is seen because UB shows a shortened duration due to intensified PVy over Eurasia caused by increased BKS sea ice. In addition, the North Atlantic SST forcing on the WACS also shows a multiple time-scale feature. Embedded in the multidecadal timescale (≥ 50 years) of AMO, the North Atlantic SST tripole (NAT) pattern can also significantly influence the Siberian cold anomaly on decadal (10–30 years) time scales not by the BKS sea-ice decline. Even during the suppressed WACS trend period (P1) from AMO+ to AMO−, a positive WACS pattern is still seen during 1960–1970, which is mainly dominated by the NAT pattern through generating a negative-phase North Atlantic Oscillation with UB.