The linkage between autumn Barents-Kara sea ice and European cold winter extremes

Abstract

Abstract. Despite intense efforts to understand the links between the Arctic region and mid-latitudes, there is no consensus on the relationship between sea ice retreat and the frequency of occurrence of mid-latitude weather extremes (e.g., cold spells, heatwaves, droughts). By tracking monthly variabilities based on observational data, we show that a decline in sea ice over the Barents-Kara Seas in autumn is related to extreme cold winters over much of Europe. The winter temperature change in Europe is a direct response to a stationary Rossby wave generated by the lower troposphere diabatic heat anomaly as a result of sea ice loss over the Barents-Kara Seas in autumn, leading to a negative phase of North Atlantic Oscillation and more frequent episodes of the atmospheric blocking over Greenland and the North Atlantic. The negative phase of the North Atlantic Oscillation and enhanced blocking are closely related and mutually reinforcing, shaping the spatial distribution of cold anomalies over much of the European continent. Our results suggest a link between the unusual retreat in Barents-Kara Sea ice during autumn and the occurrence of intense European weather extremes in subsequent winter months. Nevertheless, climate models have difficulties to capture the variability and trend of the Artic sea ice and to capture the relationship between sea ice reduction and European winter extremes. Consequently, further work on this relationship on monthly time scales will improve our understanding of the prediction of midlatitude extreme events.