“暖北极-冷欧亚”模态的变化及其气候环境效应
Variations of the “warm Arctic-cold Eurasia” pattern and the climate-environment effects
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摘要: “暖北极-冷欧亚”是冬季北极-中高纬气候变异的关键模态之一,存在于多时间尺度。2012年后,“北极增暖-欧亚变冷”趋势的减弱引发了关于北极-欧亚之间气候联系是否消失或减弱的热烈讨论。基于多源数据的诊断发现,北极-欧亚气候紧密联系的时间尺度从冬季平均向次季节转移,呈现出“暖北极-冷欧亚”前后冬位相反转增多、增强的科学事实。“暖北极-冷欧亚”模态会导致大尺度经向温度梯度减弱,形成持续性、大振幅的大气环流异常,进而触发极端寒潮的发生。更重要的是,“暖北极-冷欧亚”前后冬位相反转会驱动蒙古地区以及我国东部出现极端冷暖转换。蒙古地区作为我国重要沙源地,前后冬之间快速的冷暖反相造成地面疏松裸露,为华北超级沙尘暴提供充足物质条件。次季节尺度上的“暖北极-冷欧亚”提供了更清晰的前、后冬变化的物理图像。后冬“暖北极-冷欧亚”模态对华北霾污染也有显著影响,并在北极野火的预测中表现出关键作用。未来关于“暖北极-冷欧亚”模态的研究亟须关注趋势变化及不确定性,厘清前后冬位相反转的触发机制,改进气候模式对反转模态的模拟和预测性能,以期提升对中低纬冬春季极端气候的预测能力。Abstract: “Warm Arctic-cold Eurasia” (WACE) pattern is one of the key modes of winter Arctic-Eurasia climate variability, existing on multiple time scales. After 2012, the weakening of the “Arctic warming-Eurasia cooling” trend has sparked intense discussions on whether the Arctic-Eurasia climatic linkage has disappeared or weakened. Diagnosis analyses based on multi-source data indicate that the time scale of the close connection between the Arctic and Eurasia climates shifts from the winter-mean to subseasonal variations, presenting the increasing and strengthening phase reversal of WACE between early and late winter. WACE pattern can lead to a weakened large-scale meridional temperature gradient, forming persistent and large-amplitude atmospheric circulation anomalies, thereby triggering the extreme cold waves. More importantly, the WACE reversal can drive the extreme cold-warm transitions in the Mongolian region and eastern China. As Mongolia is a major dust source for China, rapid wintertime phase reversals lead to loose, bare ground surfaces, providing ample material conditions for severe sandstorms in North China.SThe “Warm Arctic-Cold Eurasia” on the subseasonal scale offers a clearer physical features of the variations in early and late winter. The WACE in late winter also significantly impacts the haze pollution in North China and plays a key role in predicting Arctic wildfires. Future research on WACE pattern urgently needs to focus on its trend changes and uncertainties, clarify the trigger mechanism for its phase reversal, and improve the simulation and prediction performance of climate models, in order to enhance the prediction ability for winter-spring extreme climates in mid-low latitudes.