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 Ⅱ.模式结果分析

Dynamical Role of Zonal Wind Stresses over the Tropical Pacific in the Occurring and Vanishing of El Nio Part II: Analyses of Modeling Results

为了分析 ＥＩ 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，建立一个类似于Ｚｅｂｉａｋ的简单热带海洋数值模式，在观测到的风应力异常的强迫下，模拟赤道太平洋地区 １９７１年１月至 １９９８年８月海表温度异常的变化。结果表明，模式对观测的Ｎｉｏ３区海表温度异常（ＳＳＴＡ）有很好的模拟能力。模拟和观测Ｎｉ区ＳＳＴＡ之间的相关系数可达 ０．９０。模式对 Ｅｌ Ｎｉｏ事件期间赤道太平洋海表温度异常随时间变化也有较好的模拟能力。为了分析Ｅｌ Ｎｉｏ期间ＳＳＴＡ的空间分布及其随时间变化的动力学机制，还对１９８６～１９８９年 ＥＮＳＯ循环期间赤道太平洋地区观测的 ＳＳＴＡ的传播特征及其形成机制进行了分析。模式较好地模拟出了观测到的赤道太平洋地区ＳＳＴＡ的传播特征，即从１９８６年底至１９８７年 ４月， ＳＳＴＡ具有向东传播的特征，从 １９８７年 ６月至 １９８８年 ２月具有向西传播的特征。动力学分析的结果表明，赤道中西太平洋地区的缔向风应力异常对 Ｅｌ Ｎｉｏ事件的发生和消亡具有重要作用。赤道中西太平洋地区的西风异常可强迫出东传的Ｋｅｌｖｉｎ波，这个东传的 Ｋｅｌｖｉｎ波对正 ＳＳＴＡ的东传起主要作用，当这个东传的

A simple tropical numerical ocean model similar to Zebiak's one is built in order to analyze the dynamical role of zonal wind stresses over the tropical Pacific in the occurring and vanishing of EI Nino events. The model is used to simulate the SSTA variability with time from January of 1971 to August of 1998 by the observed wind stress (FSU) forcing. The results show that the model successfully simulates the variability of SSTA in Nino3 area with time. The correlation coefficient is 0.9 between observational and modeling SSTA over Nino3 area. The model can better simulate the horizontal SSTA variability with time during EI Nino events. In order to better understand the mechanism of SSTA spatial distribution with time, as an example, we analyze the SSTA propagating characteristics and its causes in the modeling and observational results over the equatorial Pacific in the ENSO cycle between 1986 and 1989. The model better simulates the observational SSTA propagating characteristics over the equatorial Pacific. That is, the SSTA propagates eastward from the end of 1986 to April of 1987 and westward from June of 1987 to February of 1988. The model results show that the zonal wind stress anomaly over the western and middle equatorial Pacific is very important to the occurring and vanishing of EI Nino events. The wind stress anomaly over the western and middle equatorial Pacific can initiate the eastward Kelvin wave. The eastward Kelvin wave is responsible for the SSTA propagating eastward. When the Kelvin wave reaches the east boundary, the westward propagating Rossby waves are initiated because of east boundary reflection. The westward propagating Rossby waves are responsible for SSTA propagating westward over the equatorial eastern Pacific. The propagating eastward Kelvin wave and the propagating westward Rossby waves from east boundary reflection are responsible for the second peak of SSTA in EI Nino events over the east equatorial Pacific.