Abstract Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated “short waves” (typically below 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1–10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate current velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier breaching. In tidal inlets, IG waves can propagate into the back-barrier lagoon during the flood phase and induce large modulations of currents and sediment transport. Their effect appears to be smaller during the ebb phase, due to blocking by countercurrents, particularly in shallow systems. On coral and rocky reefs, IG waves can dominate over short-waves and control the hydro-sedimentary dynamics over the reef flat and in the lagoon. In harbors and semi-enclosed basins, free IG waves can be amplified by resonance and induce large seiches (resonant oscillations). Lastly, free IG waves that are generated in the nearshore can cross oceans and they can also explain the development of the Earth's “hum” (background free oscillations of the solid earth).

中文翻译：

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次引力波：从驱动机制到影响

摘要 次重力（以下简称 IG）波是表面海浪，其频率低于风产生的“短波”（通常低于 0.04 Hz）的频率。在这里，我们关注最常见的 IG 波类型，即由入射短波中存在群引起的波。三种相关机制解释了它们的产生：(1) 绑定到短波群包络的波浪的发展、聚集和释放 (2) 这些包络对短波断裂位置的调制，以及 (3) 钻孔的合并（打破波前，类似于水力跳跃）在冲浪区内。当到达浅水区 (O(1–10 m)) 时，IG 波可以将其部分能量转移回更高的频率，这一过程高度依赖于海滩坡度。在缓缓倾斜的海滩上，IG 波可以通过深度限制的破坏来耗散大量的能量。当底部非常粗糙时，例如在珊瑚礁环境中，可通过底部摩擦消耗大量能量。未消散的 IG 波能量向海反射，主要用于最低 IG 频率和陡峭的底部斜坡。这种最低 IG 频率的反射会导致驻波（也称为驻波）的产生。反射的 IG 波可以被折射捕获，从而可以形成准周期性的沿岸模式，也称为边缘波。IG 波对沿海地区的水沉积动力学具有广泛的影响。例如，它们可以调节裂口通道中的流速并强烈影响跨岸和近岸混合。在沙滩上，IG 波会强烈影响地下水位和相关的地下水流。在平缓倾斜的海滩上，尤其是在风暴条件下，IG 波可以主导跨岸沉积物运输，通常促进冲浪区内的海上运输。在风暴条件下，IG 波还会引起过度冲洗并最终促进沙丘侵蚀和屏障破坏。在潮汐入口，IG 波可以在洪水阶段传播到后障泻湖中，并引起水流和沉积物输送的大调制。由于逆流阻塞，它们的影响在退潮阶段似乎较小，特别是在浅层系统中。在珊瑚礁和岩礁上，IG 波可以支配短波，并控制礁滩和泻湖中的水沉积动力学。在港口和半封闭盆地中，自由 IG 波可以通过共振放大并引起大的 seiches（共振振荡）。最后，在近岸产生的自由 IG 波可以穿越海洋，它们也可以解释地球“嗡嗡声”（固体地球的背景自由振荡）的发展。