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Abstract:
The Chukchi Sea, on the Pacific side of the Arctic Ocean, recorded its largest ice-free area in the winter of 2017-18, a period when the Arctic Oscillation (AO) was persistently in its negative phase. In association with the negative AO, East Asia suffered its coldest winter since 1985 while the Arctic region was anomalously warm. Recent studies argued that the decline in Chukchi Sea ice forced the jet stream to meander southward over Asia and America, allowing cold air to spread there (e.g., Tachibana 2020). However, cold Asian winters are typically explained by La Niña and reduced Arctic ice in the Atlantic sector. As Chukchi Sea ice coverage has severely declined in recent years, the importance of its role with respect to these traditional factors should be investigated on a multiannual time scale in light of anticipated global warming. Here we present a statistical analysis showing that 2017-18 was the only winter since 1985 in which declining ice in the Chukchi Sea played a leading role and that previously its contribution was much smaller than those of Barents Sea ice and La Niña. A simple numerical experiment involving an anomalous heat source over the Pacific sector of the Arctic successfully simulated a cold Asia and warm Arctic. Thus, an anomalous negative AO along with the cold Asian winter of 2017-18 may be partially explained by the decline in Chukchi Sea ice. In the context of global warming, long-term forecasts of Chukchi Sea ice may improve predictions of Asian climate.
