热带东风气流中低压形成的非线性过程

The Nonlinear Process of the Depression Formation in the Tropical Easterly Flow

从有水平辐合辐散的赤道 β平面浅水方程出发 ,采用变量替换和小参数展开法 ,推导出了热带纬向气流作用下的非线性近似方程 ,给出了非线性方程孤立波解和一阶近似方程u1 、v1 、1 的形式解。由此讨论了热带东风气流中的低压形成。结果表明 :( 1 )在热带东风气流或热带东风弱切变气流中 ,可以得到低压形势结构 ;东风气流弱切变不影响低压纬向宽度 ,而对低压强度和低压中心位置有一定的影响。 ( 2 )当热带东风气流减弱时 ,低压中心位置偏北 ,低压强度增强 ,低压纬向宽度变大 ;在东风气流中 ,低压中心位于 1 5～ 2 0°N之间 。

Starting from the shallow water equations which include convergence and divergence in the equatorial beta plane, the nonlinear approximate equations in the action of tropical zonal flow are obtained by using methods of variable substitution and small parameter expansion. The solution of solitary wave in the nonlinear equation and the form solutions of u 1, v 1 and  1 in the first order approximate equations are given. Then the depression formation in tropical easterly flow is discussed. The following results are obtained. (1) The pattern structure of depression can be obtained in tropical easterly flow or in tropical easterly flow with weak shear. The weak shear of easterly flow has no influence on depression zonal width, however, it has a certain influence on strength and center position of depression. (2)When the tropical easterly flow decreases, the center position of depression moves northward, the strength of depression increases and the zonal width of depression widens. In the easterly flow, the center position of depression appears between 15°N to 20°N. The center position of depression is relatively consistent with the position of depression formation in the observational tropical easterly flow.