二层海洋赤道Kelvin波解析解模态分析

Analytical Solutions of the Two-layer Oceanic Equatorial Kelvin Wave

采用赤道β平面近似下的线性化二层海洋扰动方程组,对其中的赤道Kelvin波做解析求解,结果表明:该赤道Kelvin波共有2个模态;两者上、下层流场均为东向纬向流,振幅均在赤道处最大,并都呈经向衰减态势,两者波动均是非频散的,这些都与经典Kelvin波相同。第一模态(前者)的相速要比第二模态(后者)大2个量级,后者相速与海洋流速相近。前者是快波模态,后者是慢波模态。前者周期约为半天,后者约为1季度,并具气候意义。前、后者各层流场向高纬的衰减分别表现为缓慢和迅速,后者呈赤道俘获波形态。两模态各层位势场向高纬的衰减同流场。将后者与实际热带印度洋和太平洋的实况及诊断作对比后知,它们具有一致之处。后者能对实际赤道海洋情况以及ENSO现象做出某种解释。

Analytical solutions of oceanic equatorial Kelvin wave were achieved based on two-layer linear perturbation equations with equatorial beta-plane approximation.The results show that this equatorial Kelvin wave has two modes.The current fields of upper-layer and lower-layer of the two modes are both eastward zonal flow,which peaks at the equator and decays with the increase of latitude.The two modes are non-dispersive.All of these features are same as those of classic Kelvin wave.The phase velocity of the first mode（the former）is two orders of magnitude larger than that of the second mode（the latter）.The phase velocity of the latter was close to the ocean current speed.The former is a fast-wave mode,of which the period was about half a day,while the latter is a slow-wave mode,of which the period was about one season,and has important implications for climate.The attenuation of flow fields of first mode is much faster than that of the second mode,and the latter is more of equatorial captured wave.The meridional attenuation of the potential field in each layer of the two modes is similar to the flow field.The latter agrees well with the observed wave dynamics of the tropical Indian Ocean and Pacific Ocean,and can explain some phenomena in equatorial oceans and ENSO.