Summer Russian heat waves and their links to Greenland's ice melt and sea surface temperature anomalies over the North Atlantic and the Barents-Kara Seas

Abstract

In this paper, we examine what leads to the onset of summer Russian heat waves. The reanalysis data show that summer heat waves over west Russia have two types of spatial patterns: mid-latitude heat waves related to mid-latitude Ural blocking Ural blocking (UB) events occurring at the longitudes of 30 -70 E and at the midlatitudes of 40 -60 N, and high-latitude heat waves related to high-latitude UB events occurring at the longitudes of 50 -100 E and at the high latitudes of 50 -75 N. It is found that the two types of UB events have different dynamic origins. While the high-latitude UB results from the propagation of Rossby wave trains due to the decay of Greenland blocking, mainly related to strong ice melting over Greenland's land, the mid-latitude UB originates from the decay of North Atlantic blocking mainly related to positive extratropical North Atlantic sea surface temperature (SST) anomalies associated with a positive Atlantic Multidecadal Oscillation (AMO+). We demonstrate that the sign of the SST anomaly over the Barents-Kara Sea (BKS) influences the UB in position and strength. In particular, the impact of a positive BKS SST anomaly on the high-latitude UB is strong, which leads to a high-latitude UB through an anticyclonic anomaly over the BKS and its combination with the UB anticyclone resulting from the decay of Greenland blocking. By comparison, the effect of a BKS SST anomaly on the mid-latitude UB is relatively weak. It is further revealed that a strong Greenland ice melt, a positive BKS SST anomaly and a strong negative North Atlantic Oscillation are the precursors of high-latitude UB, whereas an extratropical AMO+ SST anomaly and a negative BKS SST anomaly are the precursors of mid-latitude UB.