Infragravity (IG) waves are expected to contribute significantly to coastal flooding and sediment transport during hurricane overwash, yet the dynamics of these low-frequency waves during hurricane impact remain poorly documented and understood. This paper utilizes hydrodynamic measurements collected during Hurricane Harvey (2017) across a low-lying barrier-island cut (Texas, U.S.A.) during sea-to-bay directed flow (i.e., overwash). IG waves were observed to propagate across the island for a period of five hours, superimposed on and depth modulated by very-low frequency storm-driven variability in water level (5.6 min to 2.8 h periods). These sea-level anomalies are hypothesized to be meteotsunami initiated by tropical cyclone rainbands. Estimates of IG energy flux show that IG energy was largely reduced across the island (79–86%) and the magnitude of energy loss was greatest for the lowest-frequency IG waves (<0.01 Hz). Using multitaper bispectral analysis, it is shown that, during overwash, nonlinear triad interactions on the sea-side of the barrier island result in energy transfer from the low-frequency IG peak to bound harmonics at high IG frequencies (>0.01 Hz). Assuming this pattern of nonlinear energy exchange persists across the wide and downward sloping barrier-island cut, it likely contributes to the observed frequency-dependence of cross-barrier IG energy losses during this relatively low surge event (<1 m).

中文翻译：

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飓风过冲过程中次重力波的转变

在飓风过冲期间，超重力波（IG）有望对沿海洪水和泥沙输送做出重大贡献，但是，飓风撞击期间这些低频波的动力学仍然缺乏文献记载和了解。本文利用了在飓风哈维（2017）期间，从海到湾的定向水流（即过度冲洗）中越过低洼的障碍岛切割（美国得克萨斯州）收集的流体动力学测量结果。观测到的IG波在整个岛上传播了五个小时，并叠加在极低频的风暴驱动的水位变化中并受其深度调制（5.6分钟至2.8小时）。这些海平面异常被认为是热带气旋雨带引发的海啸。IG能量通量的估计表明，整个岛上的IG能量大大减少（79-86％），并且对于最低频率的IG波（<0.01 Hz），能量损失的幅度最大。使用多锥双谱分析表明，在过冲过程中，势垒岛海边的非线性三合会相互作用导致能量从低频IG峰转移到高IG频率（> 0.01 Hz）下的束缚谐波。假设这种非线性能量交换模式在宽阔且向下倾斜的障壁岛切割中持续存在，则可能会在这种相对较低的浪涌事件（<1 m）期间促进观察到的跨势垒IG能量损失的频率依赖性。屏障岛海边的非线性三合会相互作用导致能量从低频IG峰转移到高IG频率（> 0.01 Hz）下的束缚谐波。假设这种非线性能量交换模式在宽阔且向下倾斜的障壁岛切割中持续存在，则可能会在这种相对较低的浪涌事件（<1 m）期间促进观察到的跨势垒IG能量损失的频率依赖性。屏障岛海边的非线性三合会相互作用导致能量从低频IG峰转移到高IG频率（> 0.01 Hz）下的束缚谐波。假设这种非线性能量交换模式在宽阔且向下倾斜的障壁岛切割中持续存在，则可能会在这种相对较低的浪涌事件（<1 m）期间促进观察到的跨势垒IG能量损失的频率依赖性。