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根据非线性的动量方程,利用多时间尺度分析方法,探讨由经向扰动与纬向扰动相互作用在热带东风中所造成的一类正压不稳定。分析表明:在零级近似下,给出了两个扰动传播的频率表达式,在一级近似下,得到了两个零级扰动振幅的解析表达式。鉴于方程中散度项的存在,当不同尺度的三个波相作用而发生共振时,仅总动能守恒,而总位拟能不守恒,这一点与无辐散大气的结论不同。两种扰动动能相互转换的机制则是涡度场与散度场的相互作用。
According to the nonlinear momentum equation, a multi-time scale analysis method is used to investigate a type of positive pressure instability caused by the interaction of meridional disturbances and latitudinal disturbances in tropical easterlies. The analysis shows that under the zero-order approximation, two frequency expressions of disturbance propagation are given. In the first-order approximation, two analytic expressions of the amplitudes of two zero-order disturbances are obtained. In view of the existence of the divergence term in the equation, when the three waves of different scales resonate, only the total kinetic energy is conserved and the total potential is not conserved, which is different from that of the non-divergent atmosphere. The mechanism of mutual transformation between two kinds of perturbation kinetic energy is the interaction between vorticity field and divergence field.