秋季北极不同海域海冰对冬季欧亚大陆气候变异的影响和机理研究

Along with the global warming, Arctic sea ice continuously declines and plays a more important role in the atmospheric circulation variation over the mid-high latitudes of Northern Hemisphere, which is favorable for the generation of severe disasters, such as freezing rain, snow and extreme cold event. Hence, Arctic sea ice variability and its possible climate effects have always been a hot topic in atmospheric research. Previous studies have revealed a possible connection between autumn Arctic sea ice anomalies and winter Eurasian climate change, however, the physical mechanisms are still unclear. In addition, little attention has been paid to the regional characteristics of autumn Arctic sea ice anomalies and the corresponding different atmospheric responses. This project plans to systematically investigate the impacts of autumn Arctic sea ice anomalies in distinct regions on the winter Eurasian climate change and the associated approaches and mechanisms through the combination of statistical analyses, dynamic diagnoses and numerical model simulation, mainly focusing on three scientific questions: (1) examine the dominant spatio-temporal features of Arctic sea ice-air interaction during boreal autumn and the impacts and mechanisms of sea ice anomalies in the distinct regions on the winter climate (surface air temperature) interannual variability over Eurasia; (2) analyze the possible process that the autumn Arctic sea ice in the distinct regions affects the winter extreme climate events over Eurasia, especially for the extreme cold events occurring in China. The results from this project have important scientific value to understand different climate response to autumn Arctic sea ice anomalies in distinct regions and help improve the prediction of medium and long term weather over Eurasia in the wintertime.

随着全球变暖加剧，北极海冰持续减少，其对北半球中高纬地区大气环流的影响愈发显著，容易引起雨雪冰冻、极端严寒等气象灾害。因此，北极海冰变异及其可能的气候效应一直是大气科学领域的热点话题。以往的研究揭示了秋季北极海冰异常与冬季欧亚大陆气候变化的可能联系，但机理尚不清晰，此外对北极海冰变化的区域性特征及其造成的不同影响也关注较少。本项目拟结合统计分析、动力诊断和数值模拟系统地分析秋季北极不同海域的海冰异常影响冬季欧亚大陆气候变化的途径和机理。重点研究：（1）秋季北极海冰-气相互作用的时空变化特征，以及不同海域的海冰异常对冬季欧亚大陆气候（温度）年际变化的不同影响和机理；（2）秋季北极不同海域的海冰异常影响冬季极端气候事件的可能过程，特别是关注发生在中国的极端低温事件。该研究对理解秋季北极不同海域海冰异常的气候效应和提高冬季欧亚大陆中长期天气的预测水平有重要的科学价值。

伴随着北极快速增暖，北极与中纬度的联系已成为当前研究的热点。作为地气系统的重要组成部分，北极海冰变化不仅能调节局地生态系统，而且通过多种复杂的物理过程将其影响扩展到中低纬地区。关于北极海冰能否影响中纬度天气气候仍存在争议。中高纬地区大气响应对海冰异常的位置十分敏感，这是以往研究不确定性的来源之一。本项目系统分析了全球变暖下秋季北极海冰变化的主要特征，着重研究了东西伯利亚-楚科奇-波弗特（EsCB）海域海冰变异对冬季欧亚气温年际变率和极端低温事件的影响和可能机理，初步比较了它与巴伦支-喀拉（BK）海域海冰气候效应的差异。.秋季北极海冰年际变异的主模态表现为EsCB海域海冰显著减少，其年际变化振幅在全球变暖下有增强趋势。观测分析和数值试验表明，秋季EsCB海域海冰减少有利于冬季欧亚中西部偏冷，并使得中国中西部极端低温频次显著增加。当海冰减少时，反气旋异常在一个月后覆盖北极、且向格陵兰-北欧延伸。行星波2波异常上传及其有关的波流相互作用一方面加强了对流层北极反气旋异常、引起早冬欧亚中部偏冷，另一方面减弱了平流层极涡。同时，瞬变波-平均流相互作用也使得北极反气旋异常向北大西洋-欧洲北部一侧发展。冬季，随着平流层异常信号在季节内下传，欧洲北部反气旋异常在7天内增强并向下游扩展，有利于北极冷空气沿超极路径快速入侵中国中西部，导致该地气温骤降。此外，平流层极涡减弱可维持至晚冬，通过向下控制再次加强北极反气旋异常、引起早春俄罗斯中部显著降温。秋季EsCB海域海冰的作用在20世纪90年代末以来显著增强，这可能与其气候态的快速消融有关。相比之下，秋季BK海域海冰减少有利于冬季欧亚北部偏冷，并使得中国西北-东北部极端低温频次显著增加，其影响范围更广、强度更强。.本项目为全面认识欧亚大陆天气气候变异机理提供了新视角，为系统理解北极海冰在气候系统中的重要作用和不确定性提供了新思路，为冬季气温、极端低温预报提供了理论依据。