垂直切变风场中声重波的谱传播

本文研究声重波在垂直切变风场中传播时谱结构的改变。根据可压缩情况下的流体力学方程组,导出垂直切变风场中大气声重波的谱方程。并指出,这个谱方程是Taylor-Goldstein方程在可压缩和任意垂直波长情况下的推广。由谱方程出发,考虑低边界上的声重波强迫为高斯谱型,采用差分方法,我们计算了ω-K_H二维空间中的高层谱响应。结果表明,在具有垂直切变的背景风场作用下,声重波的谱结构发生了改变:1.在原强迫谱所覆盖的谱区段内,一些谱成份被挖除,形成了尖锐的谱峰群;2.最大谱峰发生了偏移;3.波谱变得狭窄。这些变化是垂直切变风场对声重波谱滤波的结果。文中还将上述结论与电离层观测结果进行比较,解释了某些观测现象。

PROPAGATION OF AN ACOUSTIC GRAVITY WAVE SPECTRUM THROUGH A REGION OF VERTICAL WIND SHEAR

In this paper, the variation of spectral structure of acoustic gravity waves (AGW's) propagating through a region of vertical wind shear is investigated. By using the compressible hydrodynamic equations, a spectral equation describing propagation of AGW's in a region of vertical wind shear is derived. It is pointed out that the spectral equation is a generalized form of Taylor-Goldstein equation in the case of compressible medium and arbitrary vertical wavelength. Starting from the spectral equation, considering an AGW force with two-dimensional Gaussian spectrum at lower boundary and by using differential method, the AGW spectrum at higher level is calculated. It is shown that under the influence of the vertical wind shear, the spectral structure of AGW's is changed considerably: 1. Some spectral components in the forcing spectrum are filtered off, thus several sharp spectral peaks occur. 2. Main peak moves in frequency-wavenumber space. 3. The spectrum at higher level becomes narrower. These calculated results may explain some observed phenomena in ionosphere.