冬季乌拉尔山阻塞与东亚冬季风的联系分析

利用美国国家环境预报中心和美国大气科学研究中心(NCEP/NCAR)1948/1949~2012/2013年的逐日再分析资料,从年际变化和季节内演变两种时间尺度分析了冬季乌拉尔山阻塞与东亚冬季风的联系。结果表明,从年际变化角度,东亚冬季风综合指数(EAWMII)与冬季乌拉尔山阻塞频数显著相关,且两者的线性趋势与周期一致。当乌拉尔山阻塞频繁发生时,对流层中层西伯利亚反气旋异常,东亚大槽加深;对流层低层表现为贝加尔湖及东亚沿岸北风显著加强,中亚和东亚大部分地区地表温度降低,东亚冬季风较常年加强。乌拉尔山阻塞的由强盛到崩溃的过程对应着西伯利亚高压由加强到减弱东移的季节内演变,850 h Pa风场对应为异常北风由贝加尔湖以北逐渐影响至低纬度菲律宾以东的演变特征。

The Relationship between the Ural Blocking in Boreal Winter and the East Asian Winter Monsoon

Based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) gridded reanalysis data during 1948-2013, the relationship between the Ural blocking in boreal winter and the East Asian winter monsoon was investigated on both interannual and intraseasonal time scales. Results show that the integrated index of the East Asian winter monsoon is highly correlated with the Ural blocking frequency. In addition, they share the same linear tendency and period. The Ural blockings exert significant influences on the East Asian winter monsoon on interannual time scale. Further analyses suggest that in the winter with frequent occurrence of the Ural blocking, the anti-cyclone over Siberia at 500 hPa tends to intensify and the East Asian trough becomes deeper than normal. There are also significant signals in the lower troposphere. High frequency of the Ural blocking potentially promotes a cold EAWM (East Asia Winter Monsoon) and equatorward wind anomalies over Lake Baikal and the coastal region of East Asia. As such, a link is established between the EAWM and the Ural blocking. The intensification and eastward migration of Siberia High correspond to the peak and decaying of the Ural blocking. Meanwhile, equatorward wind anomalies develop and gradually affect a large area from Lake Baikal to the east of the Philippines.