Lagrangian transport by deep-water surface gravity wavepackets: effects of directional spreading and stratification
Lagrangian transport by deep-water surface gravity wavepackets: effects of directional spreading and stratification
复制标题
DOI：
10.1017/jfm.2019.877
复制
发表时间：
2020-01-25
影响因子：
3.7
通讯作者：
Vanneste, J.
中科院分区：
文献类型：
--
作者：
Higgins, C.;van den Bremer, T. S.;Vanneste, J.
非耗散表面重力波包的拉格朗日质量输运由斯托克斯漂移和波致回流组成。我们研究如何定向传播和密度分层影响这种质量运输的一个孤立的非耗散波包在深水中使用微扰展开。对于一个未分层的海洋，我们表明，净位移的回流是有限的，负的，相同的在所有垂直水平和成反比的深度为展向无限的数据包代表单向（二维）的海洋，但零展向本地化的数据包代表定向传播的海洋（三维）。我们解决这个差异，证明了二维（有限）和三维（零）位移之间的过渡发生在一个时间尺度上成反比的程度的定向传播。对于一个分层的海洋，我们表明，在两个维度的净位移剖面的回流随深度缓慢振荡，与波长依赖于浮力频率的比值表面波群速度，和无限的位移时，表面波包共振激发内波预测。在三维中，在分层的存在下，净位移保持为零，但有限时间的位移可能会发生明显的变化。
The Lagrangian mass transport by non-dissipating surface gravity wavepackets consists of the Stokes drift and the wave-induced return flow. We examine how directional spreading and density stratification affect this mass transport for an isolated non-dissipating wavepacket in deep water using a perturbation expansion. For an unstratified ocean, we show that the net displacement by the return flow is finite, negative, the same at all vertical levels and inversely proportional to the depth for spanwise-infinite packets representing unidirectional (two-dimensional) seas, but zero for spanwise-localised packets representing directionally spread seas (three-dimensional). We resolve this difference by demonstrating that a transition between two-dimensional-like (finite) and three-dimensional-like (zero) displacement occurs on a time scale inversely proportional to the degree of directional spreading. For a stratified ocean, we show that in two dimensions the net displacement profile by the return flow oscillates slowly with depth, with a wavelength dependent on the ratio of buoyancy frequency to the surface wave group velocity, and infinite displacements are predicted when the surface wavepacket resonantly excites internal waves. In three dimensions, the net displacement remains zero in the presence of stratification, but finite-time displacements may be appreciably altered.