海底峡谷表面重力波的演化
Evolution of surface gravity waves over a submarine canyon
摘要：
本文用三维耦合波模式研究了海底峡谷对海洋表面波传播的影响。而经典的几何光学近似预测从小入射角下的完全透射到大角度下的无透射的突然转变，完整模型预测具有部分反射/透射的更渐进的转变，其对峡谷几何形状敏感并且由小入射角和相对较短的波的消逝模式控制。大入射角的模型结果进行了比较，从周围的边缘和斯克里普斯峡谷，加利福尼亚州圣地亚哥附近，在近岸峡谷实验（NCEX）部署定向测波浮标的数据。观察到波高在短于波长的距离上跨越峡谷衰减约5倍。然而，光谱折射模型预测了大约10倍的更大的减少，因为低频分量在几何光学近似中不能穿过峡谷。耦合模式模型在峡谷上方和后方产生准确的结果。这些结果表明，虽然大部分的波浪能被折射截留在离岸边缘的峡谷，一小部分的波浪能"隧道"的峡谷。简化的模型，减少它的标准和修改后的缓坡方程也产生良好的结果，表明倏逝波模式和高阶底坡效应是次要的能量转换的波传播跨越深度等值线在大倾角。
英文摘要：
The effects of a submarine canyon on the propagation of ocean surface waves are examined with a three-dimensional coupled-mode model for wave propagation over steep topography. Whereas the classical geometrical optics approximation predicts an abrupt transition from complete transmission at small incidence angles to no transmission at large angles, the full model predicts a more gradual transition with partial reflection/transmission that is sensitive to the canyon geometry and controlled by evanescent modes for small incidence angles and relatively short waves. Model results for large incidence angles are compared with data from directional wave buoys deployed around the rim and over Scripps Canyon, near San Diego, California, during the Nearshore Canyon Experiment (NCEX). Wave heights are observed to decay across the canyon by about a factor 5 over a distance shorter than a wavelength. Yet, a spectral refraction model predicts an even larger reduction by about a factor 10, because low frequency components cannot cross the canyon in the geometrical optics approximation. The coupled-mode model yields accurate results over and behind the canyon. These results show that although most of the wave energy is refractively trapped on the offshore rim of the canyon, a small fraction of the wave energy 'tunnels' across the canyon. Simplifications of the model that reduce it to the standard and modified mild slope equations also yield good results, indicating that evanescent modes and high order bottom slope effects are of minor importance for the energy transformation of waves propagating across depth contours at large oblique angles.
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