欧亚北部2004年以来频繁冷冬的特征分析及机理初探

利用1961—2013年NCEP/NCAR发布的月平均全球再分析资料,分析了欧亚北部(40°65°N,50°-120°E)2004年以来频繁冷冬的异常特征及形成机理。结果表明:欧亚北部2004年以来冷冬频繁发生,但温度异常的空间分布,尤其中心冷区的位置有显著差异,主要表现为全区偏冷型(2005、2009、2010、2012年)和南部偏冷型(2004、2007、2011年)。全区偏冷年主要由北极涛动(AO)显著负位相所致,对应海表温度特征为北大西洋高、中、低纬度成东北-西南走向的"+、-、+"带状分布,该分布有利于北极涛动/北大西洋涛动(AO/NAO)负位相维持和增强;南部偏冷年大气内部活动异常为乌拉尔-贝加尔湖阻塞高压偏强,北极涛动/北大西洋涛动以弱正位相为主,对应主要海表温度特征为北大西洋中部偏高,其次则为太平洋年代际振荡(PDO)负位相下"类拉尼娜事件",上述海表温度异常均可促进类似欧亚遥相关的罗斯贝波列形成,有利于乌拉尔贝加尔湖阻塞高压偏强、亚洲中部多低槽活动。2004年以来欧亚北部两种类型冷冬的大气环流与海表温度均表现出与历史典型年相类似的特征。

Feature analysis and preliminary causes study of the frequent cooling winter in northern Eurasia since 2004

By using the monthly NCEP/NCAR reanalysis datasets of 1961-2013, anomalous features and potential causes of the frequent cooling winter in northern Eurasia (40°-65°N, 50°-120°E) since 2004 are analyzed in this paper. The results show that: Cooling winters took place frequently in northern Eurasia since 2004, but there is a notable difference in the distribution of temperature anomalies, especially the cold center position. It shows that 2005, 2009, 2010 and 2012 appear as whole-region-colder years, while 2004, 2007 and 2011 as south-region-colder years. The whole-region-colder years are mainly caused by the significant negative phase of the Arctic Oscillation (AO), and the corresponding SST features are zonally distributed with a Northeast-Southwest "positive-negative-positive" pattern from high latitudes, middle latitudes to low latitudes in the North Atlantic, which is beneficial to continuous negative phase of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). While south-region-colder ones were caused by the enhanced Ural-Baikal (UB) blocking with the AO/NAO generally in the weak positive phase, which mainly corresponds to the warm SST in the middle latitudes of the North Atlantic, and secondly to "similar La Niña events" under the Pacific Decadal Oscillation (PDO) negative phase.Both of the SST anomalies above can accelerate the Rossby waves which is similar to the Eurasian Teleconnections pattern and is helpful to enhanced UB blocking and trough activities in central Aisa. Either in the circulation or SST anomalies, the two types of cooling winters in northern Eurasia since 2004 are similar to the corresponding typical years in history.