The Possible Mechanisms Of Winter Arctic Sea Ice Decline And Its Relationships With Cold Events Over Mid-latitude

In this study,from the perspective of daily evolution,the mechanisms of Arctic sea ice decline and its possible relationships with its downstream cold events over mid-latitude continent are investigated based on the ERA-interim dataset during the winter season(December to February)of 1979-2016.The results of synthetic analysis show there are different mechanisms of sea ice decline over Bering Sea and Barents-Kara Sea(BKS).The sea ice decline over Bering Sea is mainly contributed by the meridional wind near the surface,followed by the downward infrared radiation(IR),and the zonal wind contributes the least.The anomalous circulation leading to the reduction of sea ice over Bering Sea is mainly composed of a wave train structure similar to the negative phase of Pacific-North American teleconnection(PNA)with a negative anomalous action over western Pacific,that is,a strong positive anomalous action center around the northern Bering Sea with three other negative anomalous action centers over the western and southern Pacific and northern North America,and the moisture convergence over Bering Sea is mostly induced by the anomalous southeasterly wind associated with an anticyclonic anomaly over Alaska Bay.For BKS,it is the zonal wind near the surface that dominates the reduction of sea ice,followed by the downward IR,and there is minimal contribution of the meridional wind.The anomalous circulation in favor of sea ice decline consists of the combination of the positive phase of North Atlantic Oscillation and the Ural blocking,and the moisture over BKS mainly comes from Norwegian Sea.On this basis,further statistical analysis shows that during the sea ice decline over Bering Sea(BKS),a cold surface air temperature anomaly simultaneously appears overNorth America(Eurasia).It is pointed out that the occurrences of sea ice decline and cold events are both the results of internal variation of atmospheric circulation,namely,under the configuration of the Northwest-Southeast dipole circulation,the warm moisture air moves northward and the cold air moves southward to induce the warming of North Pole and the cooling over its downstream continents.It is also worth to say that in addition to the cooling over Eurasia that emerges during the same periods of sea ice decline over BKS,a cold event may still occur after the sea ice has declined for about 10 days.The occurrence of this kind of cold event is closely related to the variation of turbulent heat flux(THF)after sea ice decline,that is,if the THF from ocean to atmosphere appears and maintains several days after rapid sea ice decline over BKS,a dipole structure which consists of a primary positive center of action around the Barents Sea with the other opposite-sign center of action over Eurasian continent is easily amplified,then the cold event over Eurasia is prone to occur.On the contrary,there may be no cold event if the THF from atmosphere to ocean maintains after sea ice decline over BKS.Conversely,by conducting a synthetic analysis of cold events,it is found that they may not be necessarily accompanied by the reduction of sea ice.For the North American continent,the intensity and the location of anomalous mode of atmospheric circulation will affect the degree and the period of cold events and of change in sea ice over Bering Sea.As for Eurasia,the circulation systems leading to cold events are various,and the life cycle of cold events will be longer if they are accompanied by rapid reduction of sea ice over BKS according to the comparison analysis.The above work has deepened our understanding of sea ice decline and its relationships with cold events over mid-latitude,and has certain directive significance for the prediction of the weather and climate change over mid-latitude in winter.