The winter midlatitude-Arctic interaction: effects of North Atlantic SST and high-latitude blocking on Arctic sea ice and Eurasian cooling

Abstract

In this paper, the effects of Eurasian circulation patterns such as high-latitude European blocking (HEB) and Ural blocking (UB) events on winter sea-ice concentration (SIC) in the Barents–Kara seas (BKS) and Eurasian cooling is examined to differentiate the different roles of HEB and UB in association with positive North Atlantic Oscillation (NAO+) events. A particular focus is on the SIC variability resulting from the effect of sea surface temperature (SST) near the Gulf Stream Extension (GSE) region through to the position change of Eurasian blocking. It is found that the SST shows a dipole pattern with a positive (negative) anomaly to the south (north) of the GSE, while the high SST in BKS plays a major role in the BKS SIC decline. The strengthening of North Atlantic westerly winds associated with the SST dipole tends to promote long-lived UB and HEB events associated with NAO+ to further reduce the BKS SIC, while HEB and UB depend on the prior BKS warming and UB requires stronger North Atlantic westerly winds than HEB. During UB, warm moist air from the GSE can reach the BKS to enhance downward infrared radiation (IR) via increased northward transport produced by the NAO+-UB relay. The downward IR is weak during HEB as the moisture is transported mainly into the western part of BKS, even though the NAO+-HEB relay still operates. Thus, UB leads to more pronounced BKS sea-ice declines than under HEB, although the latter still significantly contributes to the SIC loss. It is also found that the central-eastern Asian cooling occurring during UB is related to an intense, widespread SIC decline in BKS prior to the UB onset, whereas the European cooling during HEB is linked to a small SIC decline in the western part of BKS.