Linkage Between Arctic Warming And Eurasian Winter Climate And Possible Mechanisms

Under global climate warming,dramatic changes have occurred over the Arctic such as sea ice melting and surface warming.At the same time,Eurasia has seen many extreme cold winters.Previous studies have reached no consensus on whether the Arctic warming is influencing the Eurasian winter climate.This study mainly focused on the linkage between Arctic warming and Eurasian winter climate.Based on different reanalysis datasets,models' output datasets in phase 5 of the Coupled Model Intercomparison Project(CMIP5),and outputs from atmosphere-only GREENICE simulations,this study analyzed the interdecadal change in the relationship between Arctic warming and the Siberian high,revealed the important role of Arctic warming aloft on the “warm Arctic-cold Eurasia” pattern,demonstrated that Eurasian cooling in climate models is linked to the vertical distribution of Arctic warming,probed into the impact of Northern Eurasian snow cover anomaly on the warm Arctic-cold Eurasia pattern,and discussed the monthly variability of the warm Arctic-cold Eurasia pattern.The main conclusions are summarized as follows.(1)Strengthened relationship between Arctic warming and the Siberian high after the late-1990 s.Coinciding with warm anomalies over the Barents-Kara Seas in recent winters(1997–2017),the Siberian high has been significantly intensified,the East Asian jet stream has expanded westward,and an apparent Rossby wave has propagated from the Arctic to East Asia.The associated strong anomalous ascending/descending motions and divergent/convergent upper troposphere air masses over the Barents-Kara Seas and Siberian region seem to have favored the linkage between Arctic warming and the Siberian high during 1997–2017.In contrast,anomalous midlatitude atmospheric circulation and dynamic process coinciding with Arctic surface warm anomalies were barely statistically significant during 1979–1996.We further hypothesize that Arctic mid-tropospheric warming might play a crucial role for the strengthened relationship between Arctic warming and the Siberian high in boreal winter.(2)The warm Arctic-cold Eurasia pattern is linked to the vertical distribution of Arctic warming.Based on long-term reanalysis,CMIP5 multi-model simulations and atmosphere-only GREENICE simulations,we show that Eurasian below-average temperatures are more frequent in winters with deep warming compared to shallow,near-surface warming over the Barents-Kara Seas.Dramatic weakening of the midlatitude jet stream and increase in Ural blocking are more likely to occur in winters with deep Arctic warming.On synoptic scale,central Eurasia reaches the lowest temperature after the peaking of Arctic warming aloft.The lead-lag relationship indicates an interaction between deep Arctic warming and the Ural blocking.(3)Impact of autumn Northern Eurasian snow cover anomaly on the warm Arcticcold Eurasia pattern.Following reduced October Northern Eurasian(58°–68°N,30°–90°E)snow cover,a warm Arctic-cold Eurasia pattern appears in the winter,which is most significant in January.The intensified Ural high and deepened East Asian trough in January favor the warm Arctic-cold Eurasia pattern.It is further found the zonal wavenumber-1 pattern of planetary-scale waves concurrent with October Northern Eurasian snow cover anomaly extends from the surface to the upper-stratosphere.It persists in the stratosphere through November–December and propagates downward to the surface by the following January,making the connection between October snow cover anomaly and January climate possible.(4)Monthly variability of the warm Arctic-cold Eurasia pattern.The observed reversal of Eurasian temperature anomaly in different winter months(such as warm December but cold January–February)is closely associated with the reversal of Arctic temperature anomaly.And that the rapid deep Arctic warming is ahead of the reversal of Eurasian climate anomaly from warmer conditions in the early winter to colder conditions in the late winter,suggesting the potential role of Arctic warming.Note that 42.5% of the Eurasian winters during1979–2018 have experienced similar temperature anomaly reversal.It is thus necessary to investigate the monthly variability of the winter climate in the mid-and-high latitudes and its possible causes.