Internal waves are a regular feature of the open-ocean and coastal waters. As a train of internal waves propagates, their surface induced currents modulate the surface waves, generating a characteristic rough- and smooth-banded structure. While the surface expression of these internal waves is well known and has been observed from a variety of remote sensing instruments, direct quantitative observations of the directional properties of the surface gravity wave field modulated by an internal wave remain sparse. In this work, we report on a comprehensive field campaign conducted off the coast of Point Sal, California, in September 2017. Using a unique combination of airborne remote sensing observations, along with in situ surface and subsurface measurements, we investigate and quantify the interaction between surface gravity and internal wave processes. We find that surface waves are significantly modulated by the currents induced by the internal waves. Through novel observations of ocean topography, we characterize the rapid modification of the directional and spectral properties of surface waves over very short spatial scales [O(100) m or less]. Over a range of wavelengths (3–9-m waves), geometrical optics and wave action conservation predictions show good agreement with the observed wavenumber spectra in smooth and rough regions of the modulated surface waves. If a parameterization of wave action source terms is used, good agreement is found over a larger range of wavenumbers, down to 4 rad m^?1. These results elucidate properties of surface waves interacting with a submesoscale ocean current and should provide insight into more general interactions between surface waves and the fine-scale structure of the upper ocean.

表面重力波被内波调制的情况

中文摘要：内波是开阔大洋和近岸水域的一个常规特征。当一列内波传播时，其诱导的表面海流会对表面波进行调制，产生特有的粗糙和光滑相间的带状结构。虽然这些内波的表面现象是众所周知的，并且已经从各种遥感仪器中观察到了，但对被内波调制的表面重力波场的方向性的直接定量仍然很稀少。在这项工作中，我们报告了2017年9月在加州Point Sal海岸外进行的一次全面的实地观测。利用机载遥感和实地海表面和次表层测量，我们调查并定量化了海表面重力波和内波之间的相互作用。我们发现，表面重力波受到内波引发的表面海流的显著调制。通过对海洋地形的新的观测，我们描述了在非常小的空间尺度上[O(100)米或更小]，表面波的方向和光谱特性的快速改变。在一定的波长范围内（3-9米的波），几何光学和波动守恒的预测结果与观察到的调制表面波的光滑和粗糙区域的波数谱有很好的一致性。如果使用波浪作用源项的参数化，在更大的文数范围内发现良好的一致性，低至4 rad m^-1。这些结果阐明了与亚中尺度洋流相互作用的海面波的特性，并应使人们了解海面波与上层海洋的细尺度结构之间更普遍的相互作用。