北太平洋风应力与流场联合EOF的主模态分析

Main Modal Analysis of Combined EOF Diagnosis to Wind Stress and Flow Field Anomalies in North Pacific

采用了SODA资料,将海面风应力场与大洋各层流场看作一个整体做了赤道外北太平洋风应力和流场异常的联合EOF分析,此时风应力场与各层流场有相同的时间系数,这样就可揭示海气耦合的结构和演变,这是该方法的特点和优点。得到的主要结论有:诊断得到的主模态的风应力异常体现了北太平洋大气活动中心的异常,两者关系密切;在冬、春、秋三季均表征为阿留申低压的异常,在夏季则表征为副热带高压的异常。该主模态的风应力和流场异常均是PDO模态在其上的体现,且前者处海气相互作用中矛盾的主要方面,后者处次要方面,前者起着主动作用,后者则处被动状态。主模态在四季均有明显的年际变化和年代际变化;对北太平洋风场和上层流场而言,年际变化反映了ENSO的影响,而约20a的年代际变化则反映了太平洋年代际振荡(PDO)的影响。主模态中北太平洋海盆尺度的风应力异常、大洋环流异常和上层海温的动力异常这三者具有紧密的联系,这三者的连锁作用则造成了北太平洋SSTA的PDO模态;而在此大洋环流异常则起着关键中介作用。主模态的风应力异常与黑潮系统流场的异常有紧密联系;对于明显的正(负)异常,冬、夏两季135°E以东的黑潮都偏强(弱),黑潮续流则偏弱(强);对于黑潮以南的回流涡旋,冬季则偏强(弱),夏季则偏弱(强);而ENSO和PDO对黑潮流场系统的异常均有明显影响。

In this paper,a combined EOF method has been conducted for sea surface wind stress field and o- cean surface current field over North Pacific region with the SODA reanalysis dataset. The advantage of combined EOF methodology lies in that different EOF modes share the same time coefficient, which are able to reveal the structure and evolution of air-ocean coupling feature. Our work discloses that the sea surface wind stress anomalies of the dominant mode from EOF is closely related with the anomalous activities centre over North Pacific area. It is also showed the Aleutian low anomalies stay in winter, spring, and autumn seasons and the subtropical anticyclone anomalies occur in the summer. The sea surface wind stress and surface current anomalies of the first mode are reflections of Pacific Decadal Oscillation （PDO） mode. There are obvious interannual and interdecadal variations for the leading mode. For wind field and the upper current field in North Pacific, the interannual variation indicates the influence from ENSO event, whereas the interdecadal variation reveals the PDO signal. The North Pacific wind stress anomalies of the leading mode, ocean circulation anomaly and the upper ocean temperature anomalies are closely related with other. Although PDO mode of North Pacific Sea Surface Temperature anomalies is important for the coupling, ocean circulation plays a significantrole. The wind stress anomalies of the leading mode are closely associated with the Kuroshio system. For the obvious positive （negative） anomalies, Kuroshio in the east of 135 o E is strong （weak） in winter and summer, whereas the Kuroshio extension is weak （strong）. For the recireulation gyre of the south of Kuroshio, strong （weak） in winter and weak （strong） in summer. The Kuroshio flow system is also significantly influenced by ENSO and PDO.