Propagation and reflection of gravity waves in a meridionally sheared wind field
Propagation and reflection of gravity waves in a meridionally sheared wind field
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重力波在经向切变风场中的传播和反射
DOI：
10.1029/2007jd008877
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发表时间：
2008-05-06
影响因子：
4.4
通讯作者：
Yi, Fan
中科院分区：
文献类型：
--
作者：
Huang, Kai Ming;Zhang, Shao Dong;Yi, Fan
虽然重力波在垂直切变流中的传播特性已被广泛研究，但水平切变风对重力波传播的影响却鲜有报道。本文根据线性理论，讨论了纬向切变背景风场中重力波的反射特性，它与垂直切变流场中重力波的反射特性有明显的不同。通过数值模拟，给出了重力波包在经向剪切风中反射的全过程。当波到达反射层时，瞬逝区纬向扰动速度呈现瞬逝波结构，这与线性理论预言的Airy函数形式一致，而纬向扰动速度则表现出不同的波结构。纬向和纬向扰动速度的波数谱在反射过程中也表现出不同的特征。波包的能量中心在比线性理论预测的反射水平更近的位置反射。当波浪沿着（逆）纬向切变风传播时，纬向扰动动能和总波能减小（增大），纬向扰动动能增大（减小），波位和波动能之间存在能量交换。地球自转对波与背景流之间的能量传递有轻微的影响。如果反射层以外的风切变不够强，入射波的部分分量可能稳定地穿过反射层，产生透射波。大振幅重力波在切变风中传播时，会产生明显的平均流，使波的反射略有加强，表明透射率随入射波振幅的增大而略有减小。这与波浪在垂直切变风场中的反射不同，在垂直切变风场中，大振幅波浪诱导的平均流显著地增强了波浪的透射效应。在切变流中，透射率似乎主要取决于切变风和入射波的参数和谱分量。
Although the properties of gravity waves propagating in a vertically sheared flow have been extensively studied, the effects of a horizontally sheared wind on gravity wave propagations were seldom reported. In this paper, according to the linear theory, the characteristics of gravity wave reflection in a meridionally sheared zonal background wind field are discussed, which are evidently different from those of wave reflected by a vertically sheared flow. By numerical simulations, we present the whole process of a gravity wave packet reflection in a meridionally sheared wind. When the wave reaches the reflecting level, the zonal disturbance velocity in the evanescent region shows an evanescent wave configuration, which is consistent with the Airy function form predicted by the linear theory; while the meridional disturbance velocity exhibits rather different wave structures. The wave number spectra of zonal and meridional disturbance velocities also show different characteristics in the reflection process. The energy center of the wave packet is reflected in a position nearer than the reflecting level predicted by the linear theory. While the wave propagates along (against) the meridionally sheared wind, the meridional perturbation kinetic energy and total wave energy decrease (increase), whereas, the zonal perturbation kinetic energy increases (decreases); and an energy exchange between the wave potential and wave kinetic energies can be observed. Earth rotation has a slight influence on the energy transfer between the wave and the background flow. If the wind shear beyond the reflecting level isn't strong enough, part components of the incident wave may steadily penetrate across the reflecting level, and yields a transmission wave. A large amplitude gravity wave propagating in a meridionally sheared wind can obviously induce a mean flow, which strengthens slightly the wave reflection, indicating that the transmission rate slightly decreases with the increasing amplitude of the incident wave. This differs from the reflection of waves in a vertical sheared wind field, in which the mean flow induced by the large amplitude wave significantly enhances the wave transmission effect. In the meridionally sheared flow, the transmission rate seems to mainly depend on the sheared wind and the parameters and spectral components of the incident waves.