Unraveling of Impacts of Sea-Ice Loss on Extratropical Cold Winters

In recent decades, East Asia experienced severe winters frequently in spite of the continuous increase of greenhouse gases. A number of observation and modeling studies suggested that the Arctic-to-midlatitude connection might have played a central role. However, it is currently highly controversial whether the Arctic-to-midlatitude connection is driven by sea-ice forcing or result of internal atmospheric processes. Here, we try to unravel this controversial issue on the Arctic-to-midlatitude connection. Firstly, it is shown that East Asia cold winters tend to be preceded by the autumn Arctic sea ice loss, suggesting delayed impacts that cannot be explained by internal atmospheric processes. Furthermore, we find two distinct pathways of how sea-ice loss leads to extratropical cold winters. Two distinct pathways depend on the state of autumn atmospheric circulation related to the sea-ice reduction. On one hand, when the autumn sea ice loss over Barents-Kara-Laptev Seas is accompanied by anticyclonic circulation, East Asia experiences anomalously cold in early winter via intensified continent high and monsoon trough. On the other hand, when the cyclonic response is clear in the response to the sea ice loss via wind-driven sea-ice drift, significant East Asia cooling is evident in late winter because wind-driven sea-ice drift delivers a memory for delayed Arctic warming.