Directional diffusion of surface gravity wave action by ocean macroturbulence
Directional diffusion of surface gravity wave action by ocean macroturbulence
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DOI：
10.1017/jfm.2020.116
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发表时间：
2020-03
影响因子：
3.7
通讯作者：
A. B. Villas Bôas;W. Young
中科院分区：
文献类型：
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作者：
A. B. Villas Bôas;W. Young
我们使用一个多尺度展开式来平均海洋中尺度和亚中尺度特征的海面速度场集合上的波浪作用平衡方程。假设流动的统计性质是平稳的和均匀的，我们导出了表面波作用密度的扩散张量的表达式。这个扩展中的小参数是表面电流速度与重力波群速度的比值。对于各向同性电流，作用扩散系数用流动的动能谱表示。海流的Helmholtz分解为螺线形（涡旋）分量和势形（发散）分量表明，表面速度场的势形分量对波浪作用的扩散性没有影响，只有海面速度的涡旋分量才导致表面波作用的扩散。通过随机速度场集合，用蒙特卡罗射线追踪模拟验证了作用扩散率的分析结果。
We use a multiple-scale expansion to average the wave action balance equation over an ensemble of sea-surface velocity fields characteristic of the ocean mesoscale and submesoscale. Assuming that the statistical properties of the flow are stationary and homogeneous, we derive an expression for a diffusivity tensor of surface-wave action density. The small parameter in this expansion is the ratio of surface current speed to gravity wave group speed. For isotropic currents, the action diffusivity is expressed in terms of the kinetic energy spectrum of the flow. A Helmholtz decomposition of the sea-surface currents into solenoidal (vortical) and potential (divergent) components shows that, to leading order, the potential component of the surface velocity field has no effect on the diffusivity of wave action: only the vortical component of the sea-surface velocity results in diffusion of surface-wave action. We validate our analytic results for the action diffusivity by Monte Carlo ray-tracing simulations through an ensemble of stochastic velocity fields.