东北亚和北半球冬季高空切断冷涡与中国极端低温事件的联系

利用美国国家环境预测中心/国家大气研究中心再分析资料和美国气候预测中心冬季逐日温度资料，通过机器自动识别和目视相结合的方法，研究了北半球冬季500 hPa冷涡分布特征，并基于信息流因果论方法，揭示了东北亚冷涡活动与北半球其他活动区冷涡以及中国冬季极端低温事件的联系。根据冷涡活动天数随经度的变化，划分了4个活动频繁区，发现北半球冬季冷涡活动频率从大到小分别为大西洋-欧洲区（37.7%）、北太平洋区（22.35%）、东北亚区（20.95%）和北美-格陵兰区（13.77%）。北美-格陵兰区冷涡平均中心强度最强（493 dagpm），大西洋-欧洲区最弱（514 dagpm）。年际尺度上，东北亚区冷涡活动具有相对独立性，只有1月北美-格陵兰区冷涡活动天数变化在一定程度上是2月东北亚冷涡活动天数变化的原因。冷涡强年的动力学特征分析表明，东北亚区和北美-格陵兰区冷涡与北大西洋涛动正位相密切相联，北太平洋区冷涡则与北太平洋涛动正位相有联系，大西洋-欧洲区冷涡则对应北大西洋涛动和北太平洋涛动负位相。东北亚冷涡与中国极端低温联系密切，通过聚类分析界定了4类极端低温事件，发现东北-华北类、北方类和中东部类极端低温事件发生时都伴随着很强的东北亚冷涡活动。 

The relationship between winter cut-off cold vortexes in Northeast Asia and northern hemisphere as well as their connections with extreme low temperature events in China

Using the NCEP/NCAR reanalysis data and Climate Prediction Center daily temperature data, the distribution characteristics of 500 hPa cold vortex in the northern hemisphere winter are studied by automatic machine identification and visual method. Based on information flow causality theory, the relationship between cold vortex in Northeast Asia and other active regions in the northern hemisphere and the extreme cold events in China is investigated. According to the variations of cold vortex cumulative days along longitude, four active subregions are identified. It is found that the frequency of cold vortex activity in the northern hemisphere winter from large to small is 37.7% in the Atlantic-European region, 22.35% in the North Pacific region, 20.95% in Northeast Asia region and 13.77% in the North America-Greenland region. The averaged central intensity of cold vortex in the North America-Greenland region is the strongest (493 dagpm), while that in the Atlantic-European region is the weakest(514 dagpm). On interannual scale, the activities of cold vortex in Northeast Asia are relatively independent. To some extent, only cold vortex days in the North America-Greenland in January are the unstable sources of the interannual variations of cold vortex activities in Northeast Asia in February. The dynamic characteristics analysis of strong cold vortex years shows that the cold vortexes in Northeast Asia and the North America-Greenland are closely related to positive phase of the NAO, the cold vortexes in the North Pacific are closely related to positive phase of the NPO, while the cold vortexes in the Atlantic-European region correspond to negative phases of the NAO and NPO. The cold vortexes in Northeast Asia are closely related to extreme low temperature events in China. Four kinds of extreme cold events are defined by cluster analysis. It is found that the northeastern-northern type, the northern type, the south of the Yangtze River type and the mid-eastern type are accompanied by strong cold vortex activities in Northeast Asia.