2015/2016年东亚冬季及次季节气候异常的形成机理和数值模拟研究

On the background of dramatic reduction of Arctic sea ice in autumn and supper El Niño occurring in winter during 2015, most parts of Northern Hemisphere are warmer than normal in winter except that East Asia is colder than normal. Meanwhile, the day-to-day (continuous) dropping of temperature in many observational stations in China has broken the record. What’s more, the temperature anomaly in early winter is opposite to that in late winter of 2015/2016. However, the abnormal climate could not be explained by the variability of Arctic sea ice or tropical Pacific sea surface temperature. Therefore, based on several re-analysis datasets and observational datasets, we firstly explore the seasonal and sub-seasonal atmospheric circulation anomalies over East Asia in 2015/2016 winter. Secondly, by analyzing the character of atmospheric circulation anomaly, we further investigate the mechanism for the inverse temperature anomaly over East Asia between early and late winter. Finally, we explore the combined effects of autumn Arctic sea ice and winter ENSO-like sea surface temperature anomalies on the seasonal and sub-seasonal climate over East Asia in winter and further discuss the related mechanisms through dynamical analysis and model experiments by NCAR CAM5 (Community Atmospheric Model Version 5). Through this study we attempt to further understand the variability of the East Asian winter climate, and hopefully our results will be beneficial to the prediction of the East Asian winter climate.

在2015年秋季北极海冰偏少，随后冬季爆发超级El Niño事件的背景下，冬季北半球大部分地区偏暖，而东亚却偏冷。其间，中国多个台站日降温幅度、连续降温幅度突破历史纪录。此外，2015/2016年东亚前冬偏暖、后冬偏冷。单独考虑北极海冰或者热带太平洋海温都无法解释2015/2016年东亚冬季及次季节的异常气候。因此，本项目计划利用多套再分析资料和站点观测资料，首先从典型个例出发，分析2015/2016年东亚冬季及次季节的大气环流基本特征。其次，运用统计诊断方法，通过分析历史上前冬、后冬温度异常相反年份的大气环流异常，揭示东亚前冬、后冬温度异常反相变化的物理成因。最后，借助NCAR大气环流模式CAM5，探究秋季北极海冰、冬季太平洋海温（包含热带和副热带变率）对东亚冬季及次季节气候的协同影响和动力学机制。本项目旨在加深理解东亚冬季气候的变异机理，并为东亚冬季气候预测提供新的参考依据。

近年来，在秋季北极海冰偏少、冬季爆发超级El Niño事件的背景下，东亚经常观测到前冬偏暖、后冬偏冷的现象，单独考虑北极海冰或者热带太平洋海温都无法解释东亚冬季及次季节的异常气候的异常。因此，本项目利用观测资料和数值模拟试验，取得了以下重要研究成果：（1）聚焦典型个例事件，揭示了前期秋季（9-10月）北极海冰偏少，同时冬季热带中东太平洋海表温度偏高、北太平洋年代际振荡（PDO）处于正位相可能是导致东亚冬季气温前冬偏低、后冬偏高的主要影响因子；（2）10月欧亚北部积雪异常、12月北美积雪异常通过影响对流层与平流层之间准定常行星的传播、平均流-瞬变涡动相互作用进而影响东亚1月的气温变化；（3）北大西洋年代际振荡对欧亚冬季次季节气候异常的重要调制作用。本项目研究成果为东亚冬季次季节气候预测提供了新的预测因子和预测模型的理论基础。