The study addresses the question, if observed changes in terms of Arctic-midlatitude linkages during winter are driven by Arctic Sea ice decline alone or if the increase of global sea surface temperatures plays an additional role. We compare atmosphere-only model experiments with ECHAM6 to ERA-Interim Reanalysis data. The model sensitivity experiment is implemented as a set of four combinations of sea ice and sea surface temperature boundary conditions. Atmospheric circulation regimes are determined and evaluated in terms of their cyclone and blocking characteristics and changes in frequency during winter. As a prerequisite, ECHAM6 reproduces general features of circulation regimes very well. Tropospheric changes induced by the change of boundary conditions are revealed and further impacts on the large-scale circulation up into the stratosphere are investigated. In early winter, the observed increase of atmospheric blocking in the region between Scandinavia and the Urals are primarily related to the changes in sea surface temperatures. During late winter, we find a weakened polar stratospheric vortex in the reanalysis that further impacts the troposphere. In the model sensitivity study a climatologically weakened polar vortex occurs only if sea ice is reduced and sea surface temperatures are increased together. This response is delayed compared to the reanalysis. The tropospheric response during late winter is inconclusive in the model, which is potentially related to the weak and delayed response in the stratosphere. The model experiments do not reproduce the connection between early and late winter as interpreted from the reanalysis. Potentially explaining this mismatch, we identify a discrepancy of ECHAM6 to reproduce the weakening of the stratospheric polar vortex through blocking induced upward propagation of planetary waves.

中文翻译：

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北极和中纬度天气和气候之间的联系：揭示冬季海冰和海面温度变化的影响

该研究解决了这个问题：冬季观测到的北极与中纬度联系的变化是否仅由北极海冰下降驱动，或者全球海面温度的升高是否发挥了额外作用。我们将使用 ECHAM6 的纯大气模型实验与 ERA-中期再分析数据进行比较。模型灵敏度实验是作为一组海冰和海面温度边界条件的四种组合来实现的。大气环流状况是根据气旋和阻塞特征以及冬季频率变化来确定和评估的。作为先决条件，ECHAM6 很好地再现了流通体系的一般特征。揭示了边界条件变化引起的对流层变化，并研究了对平流层大规模环流的进一步影响。初冬时节，斯堪的纳维亚半岛和乌拉尔山脉之间地区大气阻塞的增加主要与海面温度的变化有关。在冬末，我们在再分析中发现极地平流层涡旋减弱，进一步影响对流层。在模型敏感性研究中，只有当海冰减少且海面温度同时增加时，才会出现气候减弱的极地涡旋。与重新分析相比，此响应有所延迟。模型中冬末对流层响应尚无定论，这可能与平流层响应较弱且延迟有关。模型实验没有重现再分析中解释的早冬和晚冬之间的联系。我们发现了 ECHAM6 的差异，通过阻止行星波引起的向上传播来重现平流层极涡的减弱，这可能解释了这种不匹配。