Preliminary simulations of internal waves and mixing generated by finite amplitude tidal flow over isolated topography

Legg, Sonya; Huijts, K.M.H.

doi:10.1016/j.dsr2.2005.09.014

Cited by 114 publications

(98 citation statements)

References 24 publications

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“…This part of parameter space is likely to be common in high-latitude coastal regions. Similar ridges have been studied with nonhydrostatic models (Nakamura et al 2000;Legg and Huijts 2006) and by observations of twolayer, hydraulically controlled ridges (Armi 1986;Farmer and Armi 1999). Because of the nonlinearity of this ridge case, no theories have been developed that can predict the wave drag that should be seen at TTP.…”

Section: Comparisons and Parameterizationsmentioning

confidence: 99%

Measurement of Tidal Form Drag Using Seafloor Pressure Sensors

Warner

MacCready

Moum

et al. 2013

Journal of Physical Oceanography

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As currents flow over rough topography, the pressure difference between the up-and downstream sides results in form drag-a force that opposes the flow. Measuring form drag is valuable because it can be used to estimate the loss of energy from currents as they interact with topography. An array of bottom pressure sensors was used to measure the tidal form drag on a sloping ridge in 200 m of water that forms a 1-km headland at the surface in Puget Sound, Washington. The form drag per unit length of the ridge reached 1 3 10 4 N m 21 during peak flood tides. The tidally averaged power removed from the tidal currents by form drag was 0.2 W m 22, which is 30 times larger than power losses to friction. Form drag is best parameterized by a linear wave drag law as opposed to a bluff body drag law because the flow is stratified and both internal waves and eddies are generated on the sloping topography. Maximum turbulent kinetic energy dissipation rates of 5 3 10 25 W kg 21 were measured with a microstructure profiler and are estimated to account for 25%-50% of energy lost from the tides. This study is among the first to measure form drag directly using bottom pressure sensors. The measurement and analysis techniques presented here are suitable for periodically reversing flows because they require the removal of a time-mean signal. The advantage of this technique is that it delivers a continuous record of form drag and is much less ship intensive compared to previous methods for estimation of the bottom pressure field.

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Section: Comparisons and Parameterizationsmentioning

confidence: 99%

Measurement of Tidal Form Drag Using Seafloor Pressure Sensors

Warner

MacCready

Moum

et al. 2013

Journal of Physical Oceanography

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“…On the other hand, for a small and narrow topographic features the internal tide response is dominated by higher modes, as reported by Legg and Huijts [52]. As such, in this "low-narrow" regime, we expect the influence of nonlinearities to be felt at comparably smaller excursion parameters.…”

Section: Discussion and Contributionsmentioning

confidence: 48%

“…We were unable to access this regime in our experiments due mainly to signal-to-noise issues at low beam angles. The lack of propagating harmonics in the experiments has the benefit, however, of being able to clearly identify whether the harmonics observed are generated directly by the topography [10], [49], or by wave-wave interactions away from the topography [74], [52]. We found significant harmonic content of the wave field that could only have been generated in the far field.…”

Section: Discussion and Contributionsmentioning

confidence: 75%

“…the first harmonic for ε = 1.73 ± 0.05), so they are confined to the neighborhood where they are generated. The spectra shown in figure 3-8, therefore, do not contain harmonics directly excited by the topography [10], but instead generated through nonlinearities, most likely at nearby wave beam reflections or crossings [86], [74], [52], [47]. The relative amplitude of the inter-harmonic content also increases with χ, although it remains weaker than the harmonic peaks.…”

Section: Results For Large Excursion Parametersmentioning

confidence: 93%

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Internal tide generation by tall ocean ridges

Mondragón¹

2009

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Internal tides are internal waves of tidal period generated by tidal currents flowing over submarine topography. Tall ridges that are nominally two-dimensional (2-D) are sites of particularly strong generation. The subsequent dissipation of internal tides contributes to ocean mixing, thereby playing an important role in the circulation of the ocean. Strong internal tides can also evolve into internal wave solitons, which affect acoustic communication, offshore structures and submarine navigation. This thesis addresses the generation of internal tides by tall submarine ridges using a combined analytical and experimental approach.The first part of the thesis is an experimental investigation of a pre-existing Green function formulation for internal tide generation by a tall symmetric ridge in a uniform density stratification. A modal decomposition technique was developed to characterize the structure of the experimental wave fields generated by 2D model topographies in a specially configured wave tank. The theory accurately predicts the low mode structure of internal tides, and reasonably predicts the conversion rate of internal tides in finite tidal excursion regimes, for which the emergence of non-linearities was notable in the laboratory.In the second part of the thesis, the Green function method is advanced for asymmetric and multiple ridges in weakly non-uniform stratifications akin to realistic ocean situations. A preliminary investigation in uniform stratification with canonical asymmetric and double ridges reveals asymmetry in the internal tide that can be very sensitive to the geometric configuration. This approach is then used with realistic topography and stratification data to predict the internal tide generated by the ridges at Hawaii and at the Luzon Strait. Despite the assumption of two-dimensionality, there is remarkably good agreement between field data, simulations and the new theory for the magnitude, asymmetry and modal content of the internal tide at these sites.The final part of the thesis investigates the possibility of internal wave attractors in the valley of double-ridge configurations. A one-dimensional map is developed to identify the existence and stability of attractors as a function of the ridge geometry. The Green function method is further advanced to include a viscous correction to balance energy focusing and dissipation along an attracting orbit of internal wave rays, and very good agreement is obtained between experiment and theory, even in the presence of an attractor.

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“…b .The excursion parameter is used to examine the nonlinearity of the waves [6,15,20]. When ǫ 2 ≪ 1, linear internal tides are generated mainly at the forcing frequency ω.O v e r subcritical topography (ǫ 1 < 1) most of the energy generation is in the first mode internal tide, while over critical or supercritical topography (ǫ 1 ≥ 1), higher modes are generated and their superposition creates internal tidal beams.…”

Section: Mechanism Of Energy Conversionmentioning

confidence: 99%

Barotropic and Baroclinic Tidal Energy

Kang¹

2012

Energy Conservation

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Preliminary simulations of internal waves and mixing generated by finite amplitude tidal flow over isolated topography

Cited by 114 publications

References 24 publications

Measurement of Tidal Form Drag Using Seafloor Pressure Sensors

Measurement of Tidal Form Drag Using Seafloor Pressure Sensors

Internal tide generation by tall ocean ridges

Barotropic and Baroclinic Tidal Energy

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