东亚冬季风及其影响的进一步研究Ⅰ.东亚冬季风变化及异常的特征

A Further Study on the East-Asian Winter Monsoon and Its Influences Part Ⅰ. Features of Variation and Anomaly

东亚冬季风是北半球冬季最活跃的大气环流系统，其活动有重要影响，其向南爆发可以越过赤道对澳大利亚夏季风起作用。但相对夏季风，人们对东亚冬季风的研究一直较少。作者首先利用Hadley中心近百年的北半球海平面气压场资料，改进提出了一个能更好表征东亚冬季风强度的指数，进一步分析研究了东亚冬季风的年际和年代际变化及其异常特征。其结果表明，东亚冬季风不仅存在着明显的年际变化，主要有准两年的振荡周期和5～7年左右的周期，还存在周期为25～30年左右以及周期为十几年的年代际变化。利用NCEP／NCAR再分析资料，采用相关分析、合成分析的方法，还系统研究了东亚冬季风异常时的大气环流特征。对比分析表明，对应强、弱东亚冬季风，大尺度环流系统（蒙古高压、阿留申低压、500hPa位势高度场等）的变化特征基本上呈反相分布；并且在强、弱东亚冬季风年，赤道地区的Hadley环流和Walker环流也出现基本反相的异常分布特征；而且赤道西太平洋有西（东）风异常出现，菲律宾以东有异常气旋（反气旋）性环流。在对异常东亚冬季风诊断分析的基础上，用一个大气环流模式（GCM）模拟了异常东亚冬季风的活动。通过对数值模拟结果的强、弱东亚冬季风进行对比分析发现，在强、弱东亚冬季风时，北半球中高纬度大气环流的结构会出现明显的变化和调整；同时，热带地区大气环流也有显著的差异。数值模拟和资料分析结果有较好的一致性，从而进一步揭示了东亚冬季风的变化和异常特征。

The East-Asian winter monsoon is the most active atmospheric circulation system in the Northern Hemisphere winter; its southward burst can cross the equator and affect the Australia. In this process, it can result in the interactions between the mid-latitude and tropical atmospheric circulation over Asian monsoon area. With this focus, we will specifically aim at better understanding the atmospheric circulation characteristics corresponding to the East Asian winter monsoon anomaly and understanding their impacts on global atmospheric circulation, weather and climate. Firstly, an intensity index to represent the East Asian winter monsoon （EAWM） was defined at first by using the Northern Hemisphere sea level pressure data of the Hadley Center and compared it with that defined by using the meridional wind at 850 hPa, then the interannual and interdecadal variations of the EAWM, and their anomalous features are investigated further through the data analyses. The results show that the EAWM exists not only clear interannual variations with the quasi-biannual and about 5-7 years periods mainly, but also interdecadal variations with 25-30 years and more than 10 years periods. According to the defined intensity index and the NCEP/NCAR reanalysis data, we used the correlation analyses and composite analyses to systematically study anomalous features of the atmospheric circulation associated the strong and weak EAWM anomaly. The comparison analyses show that for the strong/weak EAWM, there are opposite distributions of large-scale circulation systems （such as the Mongolia High, the Aleutian Low, and 500 hPa geopotential height pattern） . And for the strong/weak EAWM cases, The Hadley circulation and Walker circulation is opposite in the tropics; the zonal wind over the equatorial western Pacific has different anomalies. Furthermore, based on the data analyses on the anomalous EAWM, a General Circulation Model （GCM） numerical simulation on anomalous features of the EAWM is completed by using the SAMIL model developed in the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The simulation results show that a well climatology mean atmospheric circulation pattern and some systems at the upper troposphere and lower levels in wintertime is simulated. The simulations of strong/weak EAWM cases show that the atmospheric circulation patterns in the middle-high lati- tude have obvious change and adjustment, associated with the strong/weak EAWM. Also, tropical atmospheric circulation exists clear difference in the strong/weak EAWM. These simulated results are similar with the data analyses, so the features of variation and anomaly of the EAWM are revesled and determined further.