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Callum J. Shakespeare and Andrew McC. Hogg

1. Introduction The generation of internal waves is a vital mechanism by which energy can be fluxed downscale and ultimately support mixing in the deep ocean ( Wunsch and Ferrari 2004 ). The major sources of internal waves in the ocean are tidal flows over rough bottom topography and high-frequency winds blowing over the ocean surface ( Munk 1981 ). Geostrophic flows interacting with bottom topography are also able to generate internal lee waves ( Nikurashin and Ferrari 2011 ). In addition

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Matthew H. Alford, Ren-Chieh Lien, Harper Simmons, Jody Klymak, Steve Ramp, Yiing Jang Yang, David Tang, and Ming-Huei Chang

1. Introduction The strongest nonlinear internal waves (NLIW) in the world’s oceans occur in the South China Sea (SCS; Fig. 1 ), where their horizontal and vertical velocities can exceed 2 and 0.7 m s −1 , respectively ( Klymak et al. 2006 ). These flows and the associated downward displacements of >200 m are great enough to hamper surface and submarine navigation. In addition, their fluid speeds can exceed their wave celerities, leading to trapped cores and elevated dissipation (R.-C. Lien et

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Chunxin Yuan, Roger Grimshaw, Edward Johnson, and Xueen Chen

1. Introduction Interest in the nonlinear internal solitary waves (ISWs) that occur in the coastal ocean has been particularly strong during the last several decades, owing to their important role on the marine ecosystem, marine geology, and in coastal engineering. ISWs often have large amplitudes and strong currents, for instance, Huang et al. (2016) recorded an extreme ISW with an amplitude of 240 m and a peak westward current velocity of 2.55 m s −1 in the northern South China Sea. The

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Daniel Bourgault, David C. Janes, and Peter S. Galbraith

1. Introduction In idealized two-layer systems, when a first-mode internal solitary wave of depression approaches normally a uniformly shoaling bottom, or “internal beach,” a fraction R of its energy reflects into first-mode internal waves. The remaining energy induces other motions (e.g., boluses, swash, intrusion, etc.), is dissipated in the bottom boundary, or is converted to turbulence during wave breaking and run up. Exactly how the incident wave energy is partitioned among these

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Qiang Li, Xianzhong Mao, John Huthnance, Shuqun Cai, and Samuel Kelly

1. Introduction Conventional internal wave theories assume that background vertical stratification (−∂ B /∂ z , where B is the buoyancy) is horizontally uniform. However, this assumption is not always valid in the ocean ( Fig. 1 ). Horizontal density gradients are associated with oceanic processes dominated by the geostrophic balance. Intensified jets exist along the western boundaries (e.g., the Kuroshio in the North Pacific Ocean and Gulf Stream in the North Atlantic Ocean), forming a

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Tyler D. Hennon, Stephen C. Riser, and Matthew H. Alford

1. Introduction It has been suggested for some time that ocean stratification and meridional overturning are related to the strength of abyssal mixing ( Munk 1966 ). More recently acknowledged has been the role of the spatial variability of mixing on these processes ( Samelson 1998 ; Simmons et al. 2004 ). Despite this importance, global patterns of mixing are still relatively poorly understood. Internal waves are thought to be a key contributor to abyssal mixing ( Munk and Wunsch 1998 ). They

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Ming-Huei Chang, Ren-Chieh Lien, Yiing Jang Yang, Tswen Yung Tang, and Joe Wang

1. Introduction Synthetic aperture radar (SAR) has detected nonlinear internal waves (NLIWs) between the Luzon Strait and the continental shelf in the northern South China Sea (SCS; Fig. 1 ; Zhao et al. 2004 ). In situ observations ( Ramp et al. 2004 ; Yang et al. 2004 ; Lien et al. 2005 ; Chang et al. 2006 ) of NLIWs have been made at some locations in the SCS. Analyses suggest that NLIWs appear at tidal periodicity with amplitudes modulated at a fortnightly tidal cycle. Strong

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J. N. Moum and J. D. Nash

1. Introduction Highly resolved and rapidly sampled measurements of velocity from a fixed position on the seafloor over Oregon’s continental shelf led to a prediction of the form, sign, and magnitude of the pressure signature of nonlinear internal waves of elevation ( Moum and Smyth 2006 ). The competing effects of internal hydrostatic pressure (>0 for elevation waves), external hydrostatic pressure, and nonhydrostatic pressure (both <0 for elevation waves) led to a predicted positive seafloor

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Tomohiro Nakamura and Toshiyuki Awaji

1. Introduction The reflection and scattering of oceanic internal gravity waves off bottom topography can redistribute internal wave energy to higher vertical wavenumbers, leading to enhanced mixing near the bottom boundary. Such internal wave-induced boundary mixing has been estimated to contribute significantly to the basinwide cross-isopycnal mixing (e.g., Eriksen 1985 ; Müller and Xu 1992 ). The total amount and the distribution of cross-isopycnal mixing strongly affect the global

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Ren-Chieh Lien, Eric A. D’Asaro, Frank Henyey, Ming-Huei Chang, Tswen-Yung Tang, and Yiing-Jang Yang

1. Introduction Nonlinear internal waves (NLIWs) are often generated over topography, such as submarine ridges or continental shelves or slopes. Because of their intrinsic nonlinearity, they may propagate long distances from the generation site and retain their shape without dispersion: for example, across the deep basin of the South China Sea (SCS) ( Klymak et al. 2006 ). Fission (i.e., the disintegration of a single wave into a train of multiple waves) occurs when NLIWs are unsteady or when

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