北极涛动的纬向对称结构

运用NCEP／NCAR再分析月资料，分季节研究了北极涛动的纬向结构，以及与之相对应的纬向平均纬向风和经圈环流异常的空间结构特征，并初步探讨了北极涛动的维持机制。结果表明，北极涛动在水平方向上主要呈纬向对称的环形模态，且这种结构在冬季北极涛动的活跃期表现更为显著；而夏季纬向对称型随季节风带的北移和极涡的减弱，其节点也相应向极地移动。与北极涛动纬向对称型相联系的纬向平均纬向风在冬季表现为明显的偶极型，向上延伸到平流层；而夏季这种形态明显减弱，并只限于对流层中。与冬、夏季北极涛动纬向对称型相对应的平均经圈环流异常均表现为增强的费雷尔环流和哈得来环流，这种形势有利于北极涛动形成正反馈机制，使之得以长期维持。

Zonal Symmetry Structure of Arctic Oscillation

Using the monthly dataset of NCEP/NCAR reanalysis, the zonal structure of the Arctic Oscillation(AO) and its correlation with the zonal-mean zonal wind and the meridional circulation are studied. The results indicate that the zonal symmetry and annular mode predominate AO in wintertime and summertime, but more prominent in the AO active period in wintertime. With the shift of current zone and the attenuation of the polar vortex, the node of the summertime AO zonal symmetric mode transfers poleward compared with that of the wintertime AO. In corresponding with AO zonal symmetric mode, zonal-mean zonal wind exhibits dipolar pattern in winter which extends upward into stratosphere. In summertime this dipolar pattern weakens to great extent and limits in the bound of troposphere. Enhanced Ferrel cell and Hadley cell manifest themselves in mean meridional circulation anomaly in consistent with AO symmetric mode both in wintertime and summertime, which is in favor of the positive feedback of AO and thus the maintenance of AO mode.