El Nio事件发生和消亡中热带太平洋纬向风应力的动力作用 I.资料诊断和理论分析

Dynamical Roles of Zonal Wind Stresses over the Tropical Pacific on the Occurring and Vanishing of El Nio Part I: Diagnostic and Theoretical Analyses

通过资料分析，研究了发生在热带西太平洋海表面西风或东风应力异常与ＥｌＮｉｎｏ事件的关系。分析结果表明，对应着ＥｌＮｉｎｏ事件从发生到消亡的过程，热带西太平洋纬向风应力存在着从西风应力异常到东风应力异常的变化，并且在这个过程中，西风应力异常向东传，东风应力异常紧接其后也向东传。本文还根据观测资料的分析结果建立了理想风应力，并利用简单热带海洋模式，对热带西太平洋纬向风应力异常及其东传在ＥＮＳＯ循环中的作用进行了动力学分析，指出了它们在ＥｌＮｉｎｏ事件发生和消亡中起着重要的作用。西风应力异常通过激发出海洋中东传的暖Ｋｅｌｖｉｎ波及其在大洋东边界反射产生的暖Ｒｏｓｓｂｙ波、以及西风应力异常本身东传到赤道东太平洋，引起正的海洋混合层扰动厚度异常，导致了ＥｌＮｉｎｏ事件的发生；而异常东风应力则通过激发出东传的冷Ｋｅｌｖｉｎ波及其在大洋东边界反射产生的冷Ｒｏｓｂｙ波、以及东风应力异常本身东传到赤道东太平洋，引起负的海洋混合层扰动厚度异常，导致了ＥｌＮｉｎｏ事件的消亡。对于热带西太平洋上风应力异常的形式是东部为异常西风应力而其西部为异常东风应力，并且它们同时向东传时，则大洋东部混合层厚度对异常风应力的响应随异常东风和西风?

Based on the observational data, the relationship between El Nio and the wind stress anomalies over the tropical Pacific is diagnostically studied It shows that corresponding to the process from the occurring to the vanishing of El Nio, the wind stress over the tropical western Pacific changes from the westerly anomaly to the easterly anomaly, and the westerly anomaly and the following easterly anomaly propagate to the east By using a simple tropical oceanic model forced by ideal wind stresses set up according to the observations, dynamical analyses are made The results show that zonal wind stress anomalies over the tropical western Pacific and their eastward movements play important roles in the occurring and the vanishing of El Nio The westerly anomaly can cause the increase of the mixed layer depth in the equatorial eastern Pacific and leads El Nio to occur by means of the downwelling Kelvin wave excited in the tropical western Pacific and the downwelling equatorial Rossby wave reflected from the eastern boundary, as well as the westerly anomaly itself shifted from the west to the tropical eastern Pacific The easterly anomaly can cause the decrease of the mixed layer depth in the equatorial eastern Pacific and leads El Nio to vanish by means of the upwelling Kelvin wave excited in the tropical western Pacific and the upwelling equatorial Rossby wave reflected from the eastern boundary, as well as the easterly anomaly itself shifted from the west to the tropical eastern Pacific When the easterly anomaly is in the western part and the westerly anomaly in the eastern part over the tropical western Pacific and they both move eastward, the response of the oceanic mixed layer depth in the equatorial eastern Pacific depends on the relative strength of the anomalies, which exerts significant effect on the persistent time of El Nio