Impact Of Arctic Sea Ice Declining On The Eurasian Winter And Autumn Temperature And Its Mechanism

Arctic sea ice, as a cold source of the global, plays a central role in the climate system. The Arctic climate system has been changing dramatically since the 21st century, of which the most important indicator is the unprecedented declining of the Arctic sea ice (ASI). In this study, the impact of Arctic sea ice melt on the temperature of Eurasian winter and autumn and its related mechanisms were investigated based on the multiple observation and reanalysis data and also the numerical simulation. We examined the seasonal atmospheric temperature change in response to the Arctic sea ice loss, and showed that the strongest surface warming in Arctic occurs in winter and fall, however, the largest sea ice reduction takes place in summer and fall. The characteristics of the change of Eurasian surface air temperature (SAT) within the past 10 years and the reasons responsible for the ASI declining were also studied. Based on the studies above, we investigated the relationships between autumn ASI and winter SAT over Eurasian continent at interdecadal an and interannual timescales and found that that the winter SAT and atmospheric circulation change are associated with autumn ASI reduction through a distinct way from those related to the winter sea ice loss. At last, two mechanisms for the change of the winter SAT in response to the autumn ASI are revealed. Four primary conclusions are given as follows:(1)The decrease of Arctic sea ice and the Arctic amplification have significant seasonal variations. The southeast Arctic and northern Barents Sea are the key areas of the air-sea interaction in summer-autumn and spring-winter, respectively. Besides, the regions of largest warming are co-located with those of greatest sea ice reductions in autumn and winter, rather than summer. Note that the weakest surface warming occurs in summer. This is principally due to the sea ice melt in summer which absorbs latent heat and the warmer lower atmosphere than ocean surface. With the decreasing sea ice, more heat is transferred from the atmosphere to ocean leading to the ice-melt and upper level sea temperature warming. As a result, the near-surface warming is modest in summer. By contrast, sea ice refreezes in winter and fall and releases latent heat. Meanwhile, less ice cover causes more heat transferred from ocean to atmosphere which warms the low level air. This delayed warming effect plays an important role in the different seasonal air temperature change in Arctic.(2) In the recent 10 years, both the strongest Arctic surface warming and the most significant temperature variation occur in winter and fall, however, there are decadal drop in temperature in Eurasian winter and decadal warming in Eurasian autumn. The rapid reduction of winter Arctic sea ice plays a critical role in the recent cold winter extremes over Eurasian continent.A strong anticyclonic anomaly was generated over the mid-and high-latitude Eurasian continent together with the decadal decreasing of the whole Arctic sea ice. It favorably drove northward warm moist flow from North Atlantic into Arctic as well as southward cold flow from Arctic into mid- and high-latitude of Eurasia, and these cross-regional flows ultimately contributed to form the warm-Arctic and cold-Eurasia pattern. In autumn, the impact of the AIS declining is only Arctic amplification, there are no significant relation to the Eurasian warming.(3)The relationships between the low autumn Arctic sea ice and anomalously cold Eurasian winters are significantly different on the decadal and interannual timescales. The decadal shift is closely related to the reduction of sea ice over the whole Arctic.However, On the interannual timescale, the sea ice decreasing in the Barents Sea, the Kala sea, and the west Laptev Sea in the southwest Arctic(30°E-120°E, 75°N-85°N) had more impact on the SAT than the whole Arctic, and results in a negative phase of the North Atlantic Oscillation (NAO). The circulation change weakens prevailing westerly winds which carry warm wet air blowing from the North Atlantic to Eurasia, augments the cold winter extremes at mid-and high-latitude of the Eurasian continent.(4) The previous autumn sea ice anomalies impact the wintertime temperature over Eurasia in two pathways. On one hand, autumn sea ice anomalies can affect the ASI of the following winter, which is respondible the first variability mode, i.e., the warm Arctic-cold Eurasia pattern. On the other hand, independent on the possible temperature anomalies caused by sea ice anomalies in the following winter, autumn sea ice anomalies can trigger the second variability mode, which is similar to the NAO negative phase. Note that the ASI anomaly which can affect the second variability mode is mainly distributed in the key area (30°E-120°E,75°N-85°N), however, the averaged interdecadal sea ice declining over the whole Arctic can not lead to the second mode, and thus play little role in the winter SAT.