Internal wave generation by tidal flow over periodically and randomly distributed seamounts

Zhang, Likun; Buijsman, Maarten C.; Comino, Eva; Swinney, Harry L.

doi:10.1002/2017jc012884

Cited by 17 publications

(9 citation statements)

References 50 publications

(136 reference statements)

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“…Although mode‐1 internal tides are mainly generated by steep topographic features (Egbert & Ray, , ; Zhao et al, ), higher‐mode internal tides may be generated by the wide‐spreading small‐scale bottom features. The small‐scale gentle topographic features such as abyssal seamounts are ubiquitous in the ocean (Lefauve et al, ; Timko et al, ; Zhang et al, ). My satellite results show that these small‐scale topographic features are prone to generate higher‐mode internal tides (mode‐2 in this paper).…”

Section: Discussionmentioning

confidence: 99%

The Global Mode‐2 M₂ Internal Tide

Zhao

2018

JGR Oceans

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The mode‐2 M2 internal tide is observed from satellite altimetry. It is extracted in two steps: First, the mode‐2 component is separated from modes 1 and 3 by a bandpass filter with cutoff wavelengths of [0.85 1.35]×λ2, where λ2 is the mode‐2 wavelength; and second, three mode‐2 internal tidal waves are extracted by fitting plane waves in each 120 km by 120 km window. The satellite‐observed mode‐2 M2 internal tide underestimates its strength: It contains the phase‐locked component only, missing the time‐varying component; it contains the southbound/northbound component only, missing the eastbound/westbound component. The satellite results provide rich information on the global mode‐2 M2 internal tide. The results show that the mode‐2 M2 internal tide is ubiquitous in the ocean, and its sea surface height amplitudes are O (1 mm). The spatial patterns of mode‐1 and mode‐2 internal tides are very different. Mode 1 mainly originates at steep topographic features such as submarine ridges, but mode 2 is also generated at gentler topographic features such as abyssal seamounts and fracture zones. Mode‐1 beams propagate O (1,000 km), while mode‐2 beams can be tracked for O (100 km). Depth‐integrated energy and flux are calculated using sea surface height amplitudes and conversion functions built from the World Ocean Atlas 2013. The globally integrated energy of the mode‐2 M2 internal tide approximates to 8 PJ, about 22% of mode 1 (36.4 PJ). This work suggests that higher‐mode internal tides play an important role in the tidal energetics, in particular, over abyssal seamounts and fracture zones.

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Section: Discussionmentioning

confidence: 99%

The Global Mode‐2 M₂ Internal Tide

Zhao

2018

JGR Oceans

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“…The results presented here build on some recent internal tide process studies. The fundamental physical effect of baroclinic tide generation by action of the barotropic tide at a sloping seabed is fairly well understood, but nuances of the process are still being examined and uncovered (e.g., Zhang et al 2008;Zhang and Swinney 2014;Zhang and Duda 2013;Zhang et al 2014;Paoletti et al 2014;Zhang et al 2017). Time dependence of the ocean imparts a subtidally time-varying transfer function to the process.…”

Section: Internal Tide Generation and Propagationmentioning

confidence: 99%

Internal Tidal Modal Ray Refraction and Energy Ducting in Baroclinic Gulf Stream Currents

Duda

Lin

Buijsman

et al. 2018

Journal of Physical Oceanography

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Upstream mean semidiurnal internal tidal energy flux has been found in the Gulf Stream in hydrodynamical model simulations of the Atlantic Ocean. A major source of the energy in the simulations is the south edge of Georges Bank, where strong and resonant Gulf of Maine tidal currents are found. An explanation of the flux pattern within the Gulf Stream is that internal wave modal rays can be strongly redirected by baroclinic currents and even trapped (ducted) by current jets that feature strong velocities above the thermocline that are directed counter to the modal wavenumber vector (i.e., when the waves travel upstream). This ducting behavior is analyzed and explained here with ray-based wave propagation studies for internal wave modes with anisotropic wavenumbers, as occur in mesoscale background flow fields. Two primary analysis tools are introduced and then used to analyze the strong refraction and ducting: the generalized Jones equation governing modal properties and ray equations that are suitable for studying waves with anisotropic wavenumbers.

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“…The formation of these bedforms in the Messinian Strait was attributed to internal solitary waves generated by the interaction of tidal currents with the sill of the Messinian Strait (Droghei et al ., ). Internal waves are frequently generated by tidal flow over seamounts (Zhang et al ., ). Da Silva et al .…”

Section: Discussionmentioning

confidence: 97%

Deep‐water dunes on drowned isolated carbonate terraces (Mozambique Channel, south‐west Indian Ocean)

et al. 2019

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Subaqueous sand dunes are common bedforms on continental shelves dominated by tidal and geostrophic currents. However, much less is known about sand dunes in deep-marine settings that are affected by strong bottom currents. In this study, dune fields were identified on drowned isolated carbonate platforms in the Mozambique Channel (south-west Indian Ocean). The acquired data include multibeam bathymetry, multi-channel high-resolution seismic reflection data, sea floor imagery, a sediment sample and current measurements from a moored current meter and hullmounted acoustic Doppler current profiler. The dunes are located at water depths ranging from 200 to 600 m on the slope terraces of a modern atoll (Bassas da India Atoll) and within small depressions formed during tectonic deformation of drowned carbonate platforms (Sakalaves Seamount and Jaguar Bank). Dunes are composed of bioclastic medium size sand, and are large to very large, with wavelengths of 40 to 350 m and heights of 0Á9 to 9Á0 m. Dune migration seems to be unidirectional in each dune field, suggesting a continuous import and export of bioclastic sand, with little sand being recycled. Oceanic currents are very intense in the Mozambique Channel and may be able to erode submerged carbonates, generating carbonate sand at great depths. A mooring located at 463 m water depth on the Hall Bank (30 km west of the Jaguar Bank) showed vigorous bottom currents, with mean speeds of 14 cm sec À1 and maximum speeds of 57 cm sec À1 , compatible with sand dune formation. The intensity of currents is highly variable and is related to tidal processes (high-frequency variability) and to anticyclonic eddies near the seamounts (low-frequency variability). This study contributes to a better understanding of the formation of dunes in deep-marine settings and provides valuable information about carbonate preservation after drowning, and the impact of bottom currents on sediment distribution and sea floor morphology.

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Internal wave generation by tidal flow over periodically and randomly distributed seamounts

Cited by 17 publications

References 50 publications

The Global Mode‐2 M₂ Internal Tide

The Global Mode‐2 M₂ Internal Tide

Internal Tidal Modal Ray Refraction and Energy Ducting in Baroclinic Gulf Stream Currents

Deep‐water dunes on drowned isolated carbonate terraces (Mozambique Channel, south‐west Indian Ocean)

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Internal wave generation by tidal flow over periodically and randomly distributed seamounts

Cited by 17 publications

References 50 publications

The Global Mode‐2 M2 Internal Tide

The Global Mode‐2 M2 Internal Tide

Internal Tidal Modal Ray Refraction and Energy Ducting in Baroclinic Gulf Stream Currents

Deep‐water dunes on drowned isolated carbonate terraces (Mozambique Channel, south‐west Indian Ocean)

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The Global Mode‐2 M₂ Internal Tide

The Global Mode‐2 M₂ Internal Tide