Internal tide radiation from the Luzon Strait

Abstract This study examines the effects of the subtidal circulation on the generation and propagation of the M2 internal tide in the Philippine Sea using a primitive equation model. Barotropic to baroclinic conversion at the Luzon Strait is found to vary due to the background circulation changes over the generation site and the changing influence of remotely generated internal tides from the Mariana Arc. The varying effect of remotely generated waves results from both changing generation energy levels at the Mariana Arc and variability in the propagation of the internal tides across the Philippine Sea. The magnitude and direction of the depth-integrated baroclinic energy fluxes vary temporally, due to a combination of changing generation, propagation, and dissipation. Spatial patterns of internal tide propagation near the Luzon Strait are influenced by the locations of mesoscale eddies to the east and west of the strait. The results provide insight into the mechanisms of variability of the baroclinic tides and highlight the importance of considering both the remotely generated internal tides and the subtidal dynamics to estimate internal tide energetics.

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Impacts of Stratification Variation on the M2 Internal Tide Generation in Luzon Strait

ATMOSPHERE-OCEAN ◽

10.1080/07055900.2020.1767534 ◽

2020 ◽

Vol 58 (3) ◽

pp. 206-218

Author(s):

Zheng Guo ◽

Anzhou Cao ◽

Xianqing Lv ◽

Jinbao Song

Keyword(s):

Internal Tide ◽

Luzon Strait

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Energy Flux and Dissipation in Luzon Strait: Two Tales of Two Ridges

Journal of Physical Oceanography ◽

10.1175/jpo-d-11-073.1 ◽

2011 ◽

Vol 41 (11) ◽

pp. 2211-2222 ◽

Cited By ~ 146

Author(s):

Matthew H. Alford ◽

Jennifer A. MacKinnon ◽

Jonathan D. Nash ◽

Harper Simmons ◽

Andy Pickering ◽

...

Keyword(s):

Energy Flux ◽

Spring Tide ◽

Internal Tide ◽

Wave Pattern ◽

The Philippines ◽

Luzon Strait ◽

Net Energy ◽

Energy Fluxes ◽

Flux Divergence ◽

Turbulent Dissipation

Abstract Internal tide generation, propagation, and dissipation are investigated in Luzon Strait, a system of two quasi-parallel ridges situated between Taiwan and the Philippines. Two profiling moorings deployed for about 20 days and a set of nineteen 36-h lowered ADCP–CTD time series stations allowed separate measurement of diurnal and semidiurnal internal tide signals. Measurements were concentrated on a northern line, where the ridge spacing was approximately equal to the mode-1 wavelength for semidiurnal motions, and a southern line, where the spacing was approximately two-thirds that. The authors contrast the two sites to emphasize the potential importance of resonance between generation sites. Throughout Luzon Strait, baroclinic energy, energy fluxes, and turbulent dissipation were some of the strongest ever measured. Peak-to-peak baroclinic velocity and vertical displacements often exceeded 2 m s−1 and 300 m, respectively. Energy fluxes exceeding 60 kW m−1 were measured at spring tide at the western end of the southern line. On the northern line, where the western ridge generates appreciable eastward-moving signals, net energy flux between the ridges was much smaller, exhibiting a nearly standing wave pattern. Overturns tens to hundreds of meters high were observed at almost all stations. Associated dissipation was elevated in the bottom 500–1000 m but was strongest by far atop the western ridge on the northern line, where >500-m overturns resulted in dissipation exceeding 2 × 10−6 W kg−1 (implying diapycnal diffusivity Kρ > 0.2 m2 s−1). Integrated dissipation at this location is comparable to conversion and flux divergence terms in the energy budget. The authors speculate that resonance between the two ridges may partly explain the energetic motions and heightened dissipation.

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The Generation and Evolution of Nonlinear Internal Waves in the Deep Basin of the South China Sea

Journal of Physical Oceanography ◽

10.1175/2011jpo4587.1 ◽

2011 ◽

Vol 41 (7) ◽

pp. 1345-1363 ◽

Cited By ~ 92

Author(s):

Qiang Li ◽

David M. Farmer

Keyword(s):

South China Sea ◽

Internal Waves ◽

South China ◽

Internal Tide ◽

Luzon Strait ◽

The South China Sea ◽

The South ◽

Deep Basin ◽

Nonlinear Internal Waves ◽

China Sea

Abstract Time series observations of nonlinear internal waves in the deep basin of the South China Sea are used to evaluate mechanisms for their generation and evolution. Internal tides are generated by tidal currents over ridges in Luzon Strait and steepen as they travel west, subsequently generating high-frequency nonlinear waves. Although nonlinear internal waves appear repeatedly on the western slopes of the South China Sea, their appearance in the deep basin is intermittent and more closely related to the amplitude of the semidiurnal than the predominant diurnal tidal current in Luzon Strait. As the internal tide propagates westward, it evolves under the influence of nonlinearity, rotation, and nonhydrostatic dispersion. The interaction between nonlinearity and rotation transforms the internal tide into a parabolic or corner shape. A fully nonlinear two-layer internal wave model explains the observed characteristics of internal tide evolution in the deep basin for different representative forcing conditions and allows assessment of differences between the fully and weakly nonlinear descriptions. Matching this model to a wave generation solution for representative topography in Luzon Strait leads to predictions in the deep basin consistent with observations. Separation of the eastern and western ridges is close to the internal semidiurnal tidal wavelength, contributing to intensification of the westward propagating semidiurnal component. Doppler effects of internal tide generation, when combined with a steady background flow, suggest an explanation for the apparent suppression of nonlinear wave generation during periods of westward intrusion of the Kuroshio.

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Numerical study of M2 internal tide generation and propagation in the Luzon Strait

Acta Oceanologica Sinica ◽

10.1007/s13131-011-0144-1 ◽

2011 ◽

Vol 30 (5) ◽

pp. 23-32 ◽

Cited By ~ 3

Author(s):

Huan Li ◽

Dan Song ◽

Xueen Chen ◽

Hongbao Qian ◽

Lin Mu ◽

...

Keyword(s):

Numerical Study ◽

Internal Tide ◽

Luzon Strait

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Structure and Variability of Internal Tides in Luzon Strait

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0250.1 ◽

2015 ◽

Vol 45 (6) ◽

pp. 1574-1594 ◽

Cited By ~ 25

Author(s):

Andy Pickering ◽

Matthew Alford ◽

Jonathan Nash ◽

Luc Rainville ◽

Maarten Buijsman ◽

...

Keyword(s):

Large Scale ◽

Numerical Models ◽

Internal Tide ◽

Luzon Strait ◽

Internal Tides ◽

Mesoscale Variability ◽

Mean Flow ◽

Generation Region ◽

The Kuroshio ◽

The Western Pacific

AbstractThe Luzon Strait is the generation region for strong internal tides that radiate westward into the South China Sea and eastward into the western Pacific. Intrusions of the Kuroshio and strong mesoscale variability in the Luzon Strait can influence their generation and propagation. Here, the authors use eight moorings and two numerical models to investigate these relationships by quantifying the coherence of the diurnal and semidiurnal internal tides in the Luzon Strait. This study finds that the level of coherence of internal tide generation, energy, and energy flux is quite variable, depending on the specific location within the Luzon Strait. Large-scale spatial patterns in internal tide pressure and velocity exist across the region, shaped by the bathymetry, mean flow, and stratification. Internal tide coherence is lower (<30%) near large gradients in this pattern (predominantly along the eastern ridge), which are shifted by the variable Kuroshio and mesoscale fields. At other locations within the Luzon Strait, the internal tide is largely coherent (>80%), and simple calculations suggest that remote sources of internal tides could account for these small decreases in coherence. To the west of the Luzon Strait (away from the primary generation regions), the model suggests that diurnal internal tide energy is more coherent than semidiurnal.

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Three-Dimensional Double-Ridge Internal Tide Resonance in Luzon Strait

Journal of Physical Oceanography ◽

10.1175/jpo-d-13-024.1 ◽

2014 ◽

Vol 44 (3) ◽

pp. 850-869 ◽

Cited By ~ 56

Author(s):

Maarten C. Buijsman ◽

Jody M. Klymak ◽

Sonya Legg ◽

Matthew H. Alford ◽

David Farmer ◽

...

Keyword(s):

Three Dimensional ◽

Standing Waves ◽

Internal Tide ◽

Separation Distance ◽

Luzon Strait ◽

Flux Divergence ◽

Deep Trench ◽

3D Simulations ◽

Barotropic Flow ◽

Double Ridge

Abstract The three-dimensional (3D) double-ridge internal tide interference in the Luzon Strait in the South China Sea is examined by comparing 3D and two-dimensional (2D) realistic simulations. Both the 3D simulations and observations indicate the presence of 3D first-mode (semi)diurnal standing waves in the 3.6-km-deep trench in the strait. As in an earlier 2D study, barotropic-to-baroclinic energy conversion, flux divergence, and dissipation are greatly enhanced when semidiurnal tides dominate relative to periods dominated by diurnal tides. The resonance in the 3D simulation is several times stronger than in the 2D simulations for the central strait. Idealized experiments indicate that, in addition to ridge height, the resonance is only a function of separation distance and not of the along-ridge length; that is, the enhanced resonance in 3D is not caused by 3D standing waves or basin modes. Instead, the difference in resonance between the 2D and 3D simulations is attributed to the topographic blocking of the barotropic flow by the 3D ridges, affecting wave generation, and a more constructive phasing between the remotely generated internal waves, arriving under oblique angles, and the barotropic tide. Most of the resonance occurs for the first mode. The contribution of the higher modes is reduced because of 3D radiation, multiple generation sites, scattering, and a rapid decay in amplitude away from the ridge.

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