El Niño事件发生对南北半球大气环流异常的对称及非对称性影响及其机理分析

利用合成分析方法, 分析了1971～2003年间7个El Niño事件发生时南、北半球大气环流异常的对称与反对称特性。分析结果表明, El Niño事件发生期间, 在热带地区15°S～15°N大气环流异常以对称性为主, 但也有一定的反对称分量: 高度场异常和纬向风异常的对称性较强, 而经向风异常的反对称较强; 同时在El Niño事件演变的各阶段, 高度场异常和纬向风异常的变化较明显, 而经向风的变化较小, 高度场和风场异常在低层 (700 hPa) 和高层 (200 hPa) 呈明显的反位相分布。并且, 为探讨El Niño事件对南、北半球大气环流异常的非对称性影响的机理, 本研究进一步利用ERA－40逐日资料, 应用Hough函数分析了El Niño事件发生期间这些赤道波动的演变特征。结果表明, El Niño事件发生期间, 热带地区大气环流异常对称性较强的主要原因是对称性Rossby波异常较强, 而Rossby重力混合波异常对经向风场的反对称分量有重要作用; 并且, 研究结果还表明, 在El Niño事件发生期间, 热带东太平洋的海温正异常能够激发由对称性Rossby波和Kelvin波组成的Gill型环流异常。此外, 分析表明Hough函数在分析热带大气波动的对称性及反对称性上具有明显的优越性。

Southern-Northern Hemispheres Symmetric and Asymmetric Effect of El Niño Events on General Circulation and Analysis on Its Mechanism

This article composed seven El Niño events for the period 1971－2003, and analyzed the Southern－Northern Hemispheres symmetry of general circulation anomalies during the El Niño events. The analysis shows that the tropical (15°S－15°N) general circulation have mainly symmetric anomalies, but less antisymmetric anomalies during El Niño events. And antisymmetry of height and zonal wind anomalies is week; oppositely that of meridional wind anomalies are much stronger. In addition, there are more varieties in height and zonal wind anomalies than in meridional wind anomalies. Comparing the anomalies at 200 hPa and 700 hPa, it can be seen that the anomalies at these two levels are obviously out-of-phase. Furthermore, the Southern-Northern Hemispheres asymmetric effect of El Niño events on general circulation was studied. The Hough function was utilized to expand the observational ERA-40 daily data to equatorial waves for analyzing the evolutive characteristics of equatorial waves during El Niño events. The result shows that the reason of strong tropic symmetric anomalies of general circulation is the presence of strong symmetric Rossby waves anomalies. On the other hand, the mixed Rossby-gravity wave presents the antisymmetric anomalies, especially the meridional wind anomalies. In addition, during the El Niño events the positive sea surface temperature anomalies over the tropical eastern Pacific generated the Gill-type circulation, which consists of symmetric Rossby wave and Kelvin wave. Finally, the Hough function has advantages in analyzing the symmetry and asymmetry of the tropical atmospheric waves.