scholarly journals Observations of Tidal Internal Wave Beams at Kauai Channel, Hawaii

2009 ◽  
Vol 39 (2) ◽  
pp. 421-436 ◽  
Author(s):  
S. T. Cole ◽  
D. L. Rudnick ◽  
B. A. Hodges ◽  
J. P. Martin
Keyword(s):  
Internal Wave ◽  
Energy Flux ◽  
Momentum Flux ◽  
Internal Tides ◽  
Turbulent Dissipation ◽  
Ridge Structure ◽  
Almost Everywhere ◽  
Hawaiian Ridge ◽  
Internal Wave Generation ◽  
Almost All

Abstract To observe the across-ridge structure of internal tides, density and velocity were measured using SeaSoar and a Doppler sonar over the upper 400–600 m of the ocean extending 152 km on each side of the Hawaiian Ridge at Kauai Channel. Eighteen sections were completed in about 18 days with sampling intentionally detuned from the lunar semidiurnal (M2) tide so that averaging over all sections was equivalent to phase averaging the M2 tide. Velocity and displacement variance and several covariances involving velocity and displacement showed one M2 internal wave beam on each side of the ridge and reflection of the beams off of the surface. Theoretical ray slopes aligned with the observed beams and originated from the sides of the ridge. Energy flux was in agreement with internal wave generation at the ridge. Inferred turbulent dissipation was elevated relative to open ocean values near tidal beams. Energy flux was larger than total dissipation almost everywhere across the ridge. Internal wave energy flux and dissipation at Kauai Channel were 1.5–2.5 times greater than at the average location along the Hawaiian Ridge. The upper 400–600 m was about 1/3 to 1/2 as energetic as the full-depth ocean. Tidal beams interact with each other over the entire length of the beams causing gradients along beams in almost all covariances, momentum flux divergences, and mean flows. At Kauai Channel, momentum flux divergences corresponded to mean flows of 1–4 cm s−1.

scholarly journals Global Patterns of Low-Mode Internal-Wave Propagation. Part I: Energy and Energy Flux

2007 ◽  
Vol 37 (7) ◽  
pp. 1829-1848 ◽  
Author(s):  
Matthew H. Alford ◽  
Zhongxiang Zhao
Keyword(s):  
Internal Wave ◽  
Time Scales ◽  
Energy Flux ◽  
Internal Tide ◽  
Companion Paper ◽  
Internal Tides ◽  
Frequency Bands ◽  
Order Of Magnitude ◽  
Hawaiian Ridge ◽  
Mesoscale Currents

Abstract Extending an earlier attempt to understand long-range propagation of the global internal-wave field, the energy E and horizontal energy flux F are computed for the two gravest baroclinic modes at 80 historical moorings around the globe. With bandpass filtering, the calculation is performed for the semidiurnal band (emphasizing M2 internal tides, generated by flow over sloping topography) and for the near-inertial band (emphasizing wind-generated waves near the Coriolis frequency). The time dependence of semidiurnal E and F is first examined at six locations north of the Hawaiian Ridge; E and F typically rise and fall together and can vary by over an order of magnitude at each site. This variability typically has a strong spring–neap component, in addition to longer time scales. The observed spring tides at sites northwest of the Hawaiian Ridge are coherent with barotropic forcing at the ridge, but lagged by times consistent with travel at the theoretical mode-1 group speed from the ridge. Phase computed from 14-day windows varies by approximately ±45° on monthly time scales, implying refraction by mesoscale currents and stratification. This refraction also causes the bulk of internal-tide energy flux to be undetectable by altimetry and other long-term harmonic-analysis techniques. As found previously, the mean flux in both frequency bands is O(1 kW m−1), sufficient to radiate a substantial fraction of energy far from each source. Tidal flux is generally away from regions of strong topography. Near-inertial flux is overwhelmingly equatorward, as required for waves generated at the inertial frequency on a β plane, and is winter-enhanced, consistent with storm generation. In a companion paper, the group velocity, ĉg ≡ FE−1, is examined for both frequency bands.

scholarly journals Inferences and Observations of Turbulent Dissipation and Mixing in the Upper Ocean at the Hawaiian Ridge

2007 ◽  
Vol 37 (3) ◽  
pp. 476-494 ◽  
Author(s):  
Joseph P. Martin ◽  
Daniel L. Rudnick
Keyword(s):  
Energy Density ◽  
Internal Wave ◽  
Dissipation Rate ◽  
Internal Tide ◽  
Eddy Diffusivity ◽  
Internal Tides ◽  
Upper Ocean ◽  
Turbulent Dissipation ◽  
Hawaiian Ridge ◽  
Wave Induced

Abstract The Hawaiian Ridge is one of the most energetic generators of internal tides in the pelagic ocean. The density and current structure of the upper ocean at the Hawaiian Ridge were observed using SeaSoar and Doppler sonar during a survey extending from Oahu to Brooks Banks and up to 200 km from the ridge peak. Survey observations are used to quantify spatial changes in internal-wave-induced turbulent dissipation and mixing. The turbulent dissipation rate of kinetic energy ɛ and diapycnal eddy diffusivity Kρ are inferred from an established parameterization using internal wave shear as input. At the Kauai Channel (KC) and French Frigate Shoals/Brooks Banks sites, ɛ and Kρ decay away from the ridge with maxima exceeding minima by 5 times. At both sites, average Kρ is everywhere greater than the canonical open-ocean value of 10−5 m2 s−1. Along the ridge, ɛ and Kρ vary by up to 100 times and are largest at sites of largest numerical model internal tide energy density. In the eastern KC, Kρ > 10−3 m2 s−1 is typical in a patch more than 200 m thick located above the path of an M2 internal tide ray. An upper limit on the dissipation rate from M2 internal tides to turbulence within 50 km of the Hawaiian Ridge is roughly estimated to be in the range of 4–9 GW. At KC, the depth-integrated internal wave energy density and dissipation rate are positively correlated. Potential density inversions occur near the main ridge axis at significant topographic features. Average Kρ is larger inside inversions.

Internal Wave Generation by a Combination of Tidal and Steady Currents

2021 ◽  
Author(s):  
Xiaolin Bai ◽  
Kevin Lamb ◽  
José da Silva
Keyword(s):  
Internal Wave ◽  
Wave Generation ◽  
Satellite Observations ◽  
Internal Tides ◽  
Small Scale ◽  
Western Boundary ◽  
Boundary Current ◽  
Reanalysis Dataset ◽  
Amazon Shelf ◽  
Internal Wave Generation

<p>In the presence of topography, two main contributors for internal wave energy are tide-topography interaction transferring energy from the barotropic tide to internal tides, and lee wave generation when geostrophic currents or eddying abyssal flows interact with topography. In the past few decades, many studies considered the respective contribution of the oscillating flows or steady background flows, but few investigations have considered both.  </p><p>In this talk, we consider the joint effects of tidal and steady currents to investigate internal wave generation and propagation on the Amazon shelf, a hotspot for internal solitary wave (ISW) generation. The Amazon Shelf is off the mouth of the Amazon River in the southwest tropical Atlantic Ocean, affected by strong tidal constituents over complex bottom bathymetry and a strong western boundary current, the North Brazilian Current (NBC). Both satellite observations and numerical modelling are used in this study. Satellite observations provide a clear visualization of the wave characteristics, such as temporal and spatial distributions, propagating direction and its relation to background currents. Based on parameters from satellite observations and reanalysis dataset, we set up a model to numerically investigate the dynamics of the ISW generation. We demonstrate that the small-scale topography contributes to a rich generation of along-shelf propagating ISW, which significantly contribute to the ocean mixing and potentially cause sediment resuspension. Moreover, the ISW-induced currents also contribute to the sea surface wave breaking as observed by satellite measurements. In addition, statistics based on a decade of satellite images and numerical investigations on seasonal variations of the ISWs and the NBC improve our understanding of the generation and evolution of these nonlinear internal waves in the presence of background currents.</p>

Internal Tides and Turbulence along the 3000-m Isobath of the Hawaiian Ridge

2006 ◽  
Vol 36 (6) ◽  
pp. 1165-1183 ◽  
Author(s):  
Craig M. Lee ◽  
Thomas B. Sanford ◽  
Eric Kunze ◽  
Jonathan D. Nash ◽  
Mark A. Merrifield ◽  
...  
Keyword(s):  
Numerical Model ◽  
Dissipation Rate ◽  
Internal Tide ◽  
Internal Tides ◽  
Energy Fluxes ◽  
Density Profiles ◽  
Turbulent Dissipation ◽  
Model Average ◽  
Diapycnal Diffusivity ◽  
Hawaiian Ridge

Abstract Full-depth velocity and density profiles taken along the 3000-m isobath characterize the semidiurnal internal tide and bottom-intensified turbulence along the Hawaiian Ridge. Observations reveal baroclinic energy fluxes of 21 ± 5 kW m−1 radiating from French Frigate Shoals, 17 ± 2.5 kW m−1 from Kauai Channel west of Oahu, and 13 ± 3.5 kW m−1 from west of Nihoa Island. Weaker fluxes of 1–4 ± 2 kW m−1 radiate from the region near Necker Island and east of Nihoa Island. Observed off-ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model. Average turbulent diapycnal diffusivity K is (0.5–1) × 10−4 m2 s–1 above 2000 m, increasing exponentially to 20 × 10−4 m2 s–1 near the bottom. Microstructure values agree well with those inferred from a finescale internal wave-based parameterization. A linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km.

scholarly journals Strong Internal Waves Generated by the Interaction of the Kuroshio and Tides over a Shallow Ridge

2019 ◽  
Vol 49 (11) ◽  
pp. 2917-2934 ◽  
Author(s):  
Eiji Masunaga ◽  
Yusuke Uchiyama ◽  
Hidekatsu Yamazaki
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Energy Flux ◽  
Wave Energy ◽  
High Frequency ◽  
Deep Ocean ◽  
Internal Tides ◽  
Navier Stokes ◽  
Wave Energy Flux ◽  
The Kuroshio

AbstractThe Kuroshio and tides significantly influence the oceanic environment off the Japanese mainland and promote mass/heat transport. However, the interaction between the Kuroshio and tides/internal waves has not been examined in previous works. To investigate this phenomenon, the two-dimensional high-resolution nonhydrostatic oceanic Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) model was employed. The results show that strong internal tides propagating upstream in the Kuroshio are generated at a near-critical internal Froude number (Fri = 0.91). The upstream internal wave energy flux reaches a magnitude of 12 kW m−1, which is approximately 3 times higher than that of internal waves without the Kuroshio. On the other hand, under supercritical conditions, the Kuroshio suppresses the internal wave energy flux. The interaction of internal tides and the Kuroshio also generates upstream propagating high-frequency internal waves and solitary wave packets. The high-frequency internal waves contribute to the increase in the total internal wave energy flux up to 40% at the near-critical Fri value. The results of this study suggest that the interaction of internal tides and the Kuroshio enhances the upstream propagating internal tides under the specified conditions (Fri ~ 1), which may lead to deep ocean mixing and transport at significant distances from the internal wave generation sites.

scholarly journals On the Equilibration of Numerical Simulation of Internal Tide: A Case Study around the Hawaiian Ridge

2017 ◽  
Vol 34 (7) ◽  
pp. 1545-1563 ◽  
Author(s):  
Guang-Zhen Jin ◽  
An-Zhou Cao ◽  
Xian-Qing Lv
Keyword(s):  
Numerical Simulation ◽  
Energy Flux ◽  
Eddy Viscosity ◽  
Internal Tide ◽  
Tidal Energy ◽  
Temporal Variations ◽  
Internal Tides ◽  
Damping Coefficient ◽  
Tidal Period ◽  
Hawaiian Ridge

AbstractTo investigate the equilibration of numerical simulation (ENS) of internal tide, a three-dimensional isopycnic coordinate internal tide model is applied to simulate the M2 internal tide on idealized topography and around the Hawaiian Ridge. An idealized experiment is carried out on a Gaussian topography, and the temporal variations of the baroclinic velocity and the baroclinic energy flux are analyzed, then ENS is studied, and two criteria are presented. Moreover, the impacts of four parameters [horizontal and vertical eddy viscosity coefficients, bottom friction coefficient, and damping coefficient (to parameterize the nonhydrostatic processes in the model)] on ENS during numerical simulations, the baroclinic velocity, the baroclinic tidal energy, and the baroclinic energy flux are investigated. It appears that ENS for the M2 internal tide is more sensitive to the horizontal eddy viscosity coefficient and the damping coefficient. To further examine the criteria of ENS, a numerical experiment is carried out to simulate the M2 internal tidal constituent near the Hawaiian Ridge. The simulated surface tide shows good agreement with results from the Oregon State University tidal model and TOPEX/Poseidon (T/P) observations. The simulation results indicate that a 50 M2 tidal period (25.88 days) run is capable of ensuring ENS for the M2 internal tide in this case. In short, this paper presents a method and two criteria for examining ENS for internal tides for modelers.

scholarly journals Propagation and dissipation of internal tides in the Oslofjord

2012 ◽  
Vol 9 (1) ◽  
pp. 315-357
Author(s):  
A. Staalstrøm ◽  
E. Aas ◽  
B. Liljebladh
Keyword(s):  
Energy Dissipation ◽  
Energy Density ◽  
Internal Wave ◽  
Energy Flux ◽  
Internal Tides ◽  
Mixing Efficiency ◽  
New Information ◽  
Order Of Magnitude ◽  
Perturbation Pressure ◽  
Velocity Pressure

Abstract. Observations of velocity, pressure, temperature and salinity in the inner Oslofjord have been analysed. The data is used to provide new information about energy dissipation and mixing efficiency of internal tides generated by tidal current across the Drøbak Sill. The ratio between the observed amplitude of the internal wave in the pycnocline and the amplitude of the surface elevation is in the range 38 ± 6 at a distance of 1 km inside the sill and 11 ± 2 at 10 km. The energy flux of the internal wave propagating from the Drøbak Sill into the inner fjord is estimated to vary in the range 155–480 kW. This is the same order of magnitude as the estimated baroclinic energy loss (250 kW). Approximately 40–70% of this energy flux is dissipated within a distance of 7 km from the sill. The mixing efficiency is estimated to 0.09–0.11 based on energy density and group velocity, and 0.22–0.26 based on perturbation pressure and baroclinic velocity. These numbers are larger than earlier estimates. Only a fraction in the range 0.01–0.03 is transferred to work against buoyancy in the first basin within a distance of 7 km from the sill.

Estimating Internal Wave Energy Fluxes in the Ocean

2005 ◽  
Vol 22 (10) ◽  
pp. 1551-1570 ◽  
Author(s):  
Jonathan D. Nash ◽  
Matthew H. Alford ◽  
Eric Kunze
Keyword(s):  
Internal Wave ◽  
Energy Flux ◽  
Wave Energy ◽  
Energy Fluxes ◽  
Near Surface ◽  
Data Limitations ◽  
Pressure Anomaly ◽  
Internal Wave Generation ◽  
Hydrostatic Balance ◽  
Wave Induced

Abstract Energy flux is a fundamental quantity for understanding internal wave generation, propagation, and dissipation. In this paper, the estimation of internal wave energy fluxes 〈u′p′〉 from ocean observations that may be sparse in either time or depth are considered. Sampling must be sufficient in depth to allow for the estimation of the internal wave–induced pressure anomaly p′ using the hydrostatic balance, and sufficient in time to allow for phase averaging. Data limitations that are considered include profile time series with coarse temporal or vertical sampling, profiles missing near-surface or near-bottom information, moorings with sparse vertical sampling, and horizontal surveys with no coherent resampling in time. Methodologies, interpretation, and errors are described. For the specific case of the semidiurnal energy flux radiating from the Hawaiian ridge, errors of ∼10% are typical for estimates from six full-depth profiles spanning 15 h.

Dynamics and energetics of nonlinear internal wave around a double-canyon system

2020 ◽  
Author(s):  
Qun Li
Keyword(s):  
Continental Shelf ◽  
Internal Wave ◽  
Energy Flux ◽  
Internal Tide ◽  
Internal Tides ◽  
Flux Divergence ◽  
Wave Regime ◽  
Nonlinear Internal Wave ◽  
The North ◽  
Shelf Slope

<p>The continental shelf/slope northeastern Taiwan is a ‘hotspot’ of nonlinear internal wave (NLIW). The complex spatial pattern of NLIW indicates the complexity of the source and the background conditions. In this talk, we investigated the dynamic and energetics of the internal tide (IT) and NLIW around this region based on a 3D high resolution nonhydrostatic numerical model. Special attention is paid on the role of two main topographic features-the Mien-Hua Canyon and the North Mien-Hua Canyon, which are the energetic sources for ITs and NLIW.</p><p>The complex IT field is excited by the double-Canyon system and the rotary tidal current. ITs from different sources and formation time interference with each other further strengthen the complexity. The area-integrated energy flux divergence (the area-integrated dissipation rate) is ~0.45GW (~0.28GW) and ~0.26 GW (~0.17 GW) over the Mien-Hua Canyon and the North Mien-Hua Canyon, respectively. Along with the energetic internal tides, large-amplitude NLIW and trains are also generated over the continental shelf and slope region. The amplitude of the NLIW can reach to about 30 m on the continental slope with a water depth of 130 m and shows similar spatial complexity, which is consistent with in situ and satellite observations. Further analysis shows that the dominant generation mechanism of the NLIW belongs to the mixed tidal-lee wave regime. In addition, the dynamic processes can be significantly modulated by the Kuroshio. With the present of Kuroshio, the energy flux of the M2 internal tide shows a distinct gyre pattern and strengthens over the double canyon system, which is more close to the mooring observations and previous study.</p>

scholarly journals Global Patterns of Diapycnal Mixing from Measurements of the Turbulent Dissipation Rate

2014 ◽  
Vol 44 (7) ◽  
pp. 1854-1872 ◽  
Author(s):  
Amy F. Waterhouse ◽  
Jennifer A. MacKinnon ◽  
Jonathan D. Nash ◽  
Matthew H. Alford ◽  
Eric Kunze ◽  
...  
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Dissipation Rate ◽  
Wave Generation ◽  
Wave Power ◽  
Turbulent Dissipation ◽  
Turbulent Dissipation Rate ◽  
Diapycnal Diffusivity ◽  
Internal Wave Generation ◽  
O 10

Abstract The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10−4) m2 s−1 and above 1000-m depth is O(10−5) m2 s−1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.

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