西太平洋暖池形成与维持的动力学机制

建立了一个简单海气耦合模式,其中大气垂直分为两层,为-β平面近似线性模式。在非绝热加热项中包含了对流凝结潜热与大尺度流场之间相互作用的CISK机制以及蒸发、感热与扰动风场之间的反馈机制,并考虑了平均东风区和西风区的不同。由于只研究大气的平均纬向运动,故模式大气中仅含有Kelvin波。海洋模式为一约化重力模式,在一定条件下采用准地转近似,模式海洋中仅保留了Rossby波。对这一海气耦合模式进行特征波动分析,发现海气耦合并不显著改变大气波动的性质。在中东太平洋的平均东风区,大气的Kelvin波仍然增幅和东传。在平均西风区,大气Kelvin波振幅衰减。但耦合作用却使海洋Rossby波的性质发生变化,且波长超过某一临界波长Le的Rossby波的振幅增长。在平均东风区,结论相论。这一理论说明西太平洋暖池的形成与海洋Rossby波有关。在东太平洋,由于是平均东风区,短的Ross-by波振幅增长,不能形成水平尺度很大的“暖池”。而在平均西风的西太平洋区,有可能形成水平尺度很大的“暖池”。

STUDY OF FORMATION AND MAINTENANCE MECHANISM OF THE WEST PACIFIC WARM POOL

In this work a simple coupled air-sea model is developed. The atmosphere is a linear beta-plane approximation model which is devided into two-layers vertically . The interaction between convective condensational heating and large scale flow as well as the feedback between evaporation, sensible heating and perturbation wind is considered in the diabatic heating term . Also,the difference between the easterly and westerly regions in the parameterization of evaporation and sensible heating is taken into consideration. As we only consider the zonal motion of the tropical atmosphere , so only the Kelvin wave is included in the model atmosphere. The ocean is a reduced gravity model. Within a limitation the geostrophic approximation can be applied, therefore only the Rossby wave is kept in the model ocean. Through the eigenmode analysis of this coupled model ,it is shown that the coupled interaction between air and sea does not change the characteristics of the atmospheric wave significantly. In the mean easterly region of the east Pacific, the atmospheric Kelvin wave still enhances its amplititude and expands eastward. In the mean westerly region the amplititude of the atmospheric Kelvin wave damps. However . the coupling causes the characteristics of the oceanic Rossby wave to change significantly . In the mean westerly region . the ampli-tiude of long Rossby wave whose wave length is larger than a critical value expands ,but the amplititude of short Rossby wave damps. In the mean easterly region the conclusion is opposite. This theory shows that the formation of the west Pacific warm pool is related to oceanic Rossby wave. In the mean easterly region of the east Pacific the amplititude of short Rossby wave enhances, so there is no large "warm pool "in that region . On the contrary, perhaps there may form a large "warm pool"in the west Pacific .