Atmospheric precursors of and response to anomalous Arctic sea ice in CMIP5 models
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This study examines pre-industrial control simulations from CMIP5 climate models in an effort to better understand the complex relationships between Arctic sea ice and the stratosphere, and between Arctic sea ice and cold winter temperatures over Eurasia. We present normalized regressions of Arctic sea-ice area against several atmospheric variables at extended lead and lag times. Statistically significant regressions are found at leads and lags, suggesting both atmospheric precursors of, and responses to, low sea ice; but generally, the regressions are stronger when the atmosphere leads sea ice, including a weaker polar stratospheric vortex indicated by positive polar cap height anomalies. Significant positive midlatitude eddy heat flux anomalies are also found to precede low sea ice. We argue that low sea ice and raised polar cap height are both a response to this enhanced midlatitude eddy heat flux. The so-called “warm Arctic, cold continents” anomaly pattern is present one to two months before low sea ice, but is absent in the months following low sea ice, suggesting that the Eurasian cooling and low sea ice are driven by similar processes. Lastly, our results suggest a dependence on the geographic region of low sea ice, with low Barents–Kara Sea ice correlated with a weakened polar stratospheric vortex, whilst low Sea of Okhotsk ice is correlated with a strengthened polar vortex. Overall, the results support a notion that the sea ice, polar stratospheric vortex and Eurasian surface temperatures collectively respond to large-scale changes in tropospheric circulation.
Key wordssea ice–atmosphere coupling stratosphere–troposphere coupling atmospheric circulation Eurasian climate
本文利用第五次耦合模式比较计划(CMIP5)工业革命前对照实验的模式模拟结果, 考察了北极海冰与对流层大气,及其与欧亚冷冬的联系. 对北极海冰与大气环流进行超前滞后回归分析发现, 大气环流既是海冰异常的前兆因子同时也存在大气对海冰的滞后响应. 总体来说, 大气环流(如平流层极涡)异常超前于海冰异常的回归信号相对更强. 对海冰减退而言, 其前期中纬度涡动热通量出现显著正异常. 海冰减少和极盖位势高度是对前期中纬度强涡动热通量的响应. “极地热大陆冷”异常型也超前海冰减退异常1-2个月, 而在其之后消失, 表明欧亚冷异常和低海冰异常一样, 也是由中纬度强涡动热通量所控制. 本文结果还指出与大气环流异常相关的海冰异常的地理依赖性, 比如巴伦之海-喀拉海海冰减少之前往往出现平流层极涡减弱, 而鄂霍次克海海冰减少则对应着极涡增强. 总之, 从本文对大气超前一面的讨论结果而言, 海冰、平流层极涡和欧亚表面温度等的异常是对对流层大尺度大气环流的响应.
关键词海冰-大气耦合 平流层对流层相互作用 大气环流 欧亚气候
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This work was supported by the Natural Environment Research Council (Grant No. NE/M006123/1). The authors would also like to acknowledge the assistance of Philip SANSOM in selecting the subset of CMIP5 models.
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