利用EOF相空间分析东亚梅雨旱涝长期过程的初步研究

A Preliminary Study of the Meiyu Long-Range Processes in EOF Phase Space

利用非线性动力学中的相空间概念，分析了梅雨旱涝３～５年循环的长期过程。对全球热带 ８５０ ｈＰａ的纬向风场距平所作的 ＥＯＦ，第 １特征向量显示Ｔ Ｗａｌｋｅｒ环流异常在赤道球圈上的分布；第２特征向量主要显示热带一副热带之间的环流异常的经向分布。在第１时间系数和第２时间系数所定义的二维相空间中，由相轨线分析，得到梅雨涝年主要集中于第２象限，而旱年则相对多在第４象限。说明梅雨旱涝年际变异的主导模态和热带大气环流的主要特征向量有着密切的关联。它们显示了以３～５年时间尺度的大气环流演变的长期特征性过程。

By using the EOF phase space analysis, the long-range processes of the circulation cycle over the global tropical belt are studied and the relationship between them and Meiyu cycle is emphasized, The monthly zonal wind anomalies are represented by the normalized expansion coefficients of EOFs, and a 2-dimensional phase space is constructed by the 2 leading EOFs. The phase points successively finish closed loop during each cycle of the 3- 5 year oscillation. The 1st leading term F1 shows a distinct zonal nonuniform distribution, a strong negative center is located in the central-eastern Pacific and a positive center over the equatorial Indian Ocean, the E2 mode mainly exhibits a meridianal nonuniform distribution. When the phase points are located at the 2nd octangle, F1 <0, F2 >0, these dates are charecterized by westerlies over subtropical western Pacific, leading to large amount of Meiyu precipitation. Conversely, drought summer may be favoured for the 4th octangle, E1 >0,E2<0.