本世纪北极海冰突变的机理及其气候效应

The Arctic climate system has undergone an abrupt shift since the end of the last century. The Arctic Oscillation (AO) declines from a strong positive phase to an almost neutral state with its spatial pattern changed. The Arctic surface temperature, however, has soared in association with the abrupt acceleration of the Arctic sea ice retreat both in summer and in winter. This indicates that the Arctic climate may enter a new regime that more thermally driven by the ice-albedo feedback rather than by the atmospheric internal variability. Many previous studies suggested that the Arctic sea ice decline impacts not only the Arctic climate change, but also the mid-latitude weather and climate through its modulation on the polarity of AO. The causes of the fast Arctic sea ice loss and the responses of large-scale atmospheric circulation, however, are not fully understood so far..In this project, the satellite dataset as well as the atmospheric and oceanic assimilated dataset are applied to investigate the Arctic sea ice change in recent decade in terms of its temporal and spatial features and its mechanisms. We focus on the Barents and Kara Seas to reveal the ocean-sea ice-atmosphere interaction processes under the background of Arctic climate shift. Furthermore, we plan to explore the atmospheric response and dynamical adjustment to the underlying sea ice forcing and depict the mechanisms and physical processes that accounts for the remote impacts of Arctic sea ice on the mid-latitude climate. On the basis of data analyses, we further evaluate the CMIP5 climate models through their performances on the atmospheric response to Arctic sea ice loss, and propose suggestions on improving the model simulation effects.

北极气候在上世纪末开始发生了快速突变，北极涛动振幅减弱且空间模态改变，北极近地面增暖加速，北极冬夏季海冰均呈现加速缩减的趋势，这意味着北极气候开始脱离大气自然变率的控制而逐渐受到海冰-反照率反馈机制的影响。很多研究表明北极海冰的快速减退不仅影响北极气候变化，还通过对北极涛动位相的调制而对北半球中纬度天气气候产生一定影响。迄今为止，我们对于北极海冰突变的原因及其引起大尺度大气环流响应的动力机制知之甚少。.本项目采用卫星观测资料、大气和海洋同化资料相结合，探讨近十几年来北极海冰突变的时空特征及主要原因。重点关注巴伦支海和喀拉海区域，揭示在北极气候突变背景下这一海区海-气-冰相互作用过程。在此基础上，研究北极海冰迅速缩减对中纬度天气气候的影响及相应的物理机制，并通过对CMIP5气候模式结果的统计分析来评估气候模式对大气响应海冰变化的相关物理过程的模拟水平，为改进气候模式提出合理建议。

北极海冰从上世纪末开始加速减退，引发北极气候增暖放大效应和大气北极涛动(AO)模态的位相转变。为厘清北极海-气-冰相互作用的物理过程，充分认识和理解海冰快速变化的气候效应，本项目综合多种资料对北极海冰快速变化的时空特征、机理和气候效应进行细致地分析和探索。项目研究成果揭示海冰变异具有显著的区域和季节性：在太平洋扇区，春季白令海海冰年代际振荡和夏季楚科奇海海冰的快速减退是近年来北极冰盖季节循环振幅增大的原因；其中春季白令海海冰年代际振荡的主要原因很可能是受到北太平洋流涡振荡(NPGO)年代际突变的影响。而在大西洋扇区，秋冬季巴伦支-卡拉海海冰异常对大气具有很强的反馈能力。我们详细阐述了巴伦支-卡拉海海冰的热力效应及相应的大气动力调整过程、传播途径直至北极涛动位相的稳定；并建立了合理的评估系统，量化评估气候模式模拟海冰变化和北极涛动模态的能力，为提高海冰可预报性和改进气候模式提供了理论依据。