scholarly journals Turbulence Asymmetries in Bottom Boundary Layer Velocity Pulses Associated with Onshore-Propagating Nonlinear Internal Waves

2020 ◽  
Vol 50 (8) ◽  
pp. 2373-2391 ◽  
Author(s):  
Johannes Becherer ◽  
James N. Moum ◽  
John A. Colosi ◽  
James A. Lerczak ◽  
Jacqueline M. McSweeney
Keyword(s):  
Internal Waves ◽  
Residence Time ◽  
Surf Zone ◽  
Internal Tide ◽  
Inner Shelf ◽  
Bottom Boundary ◽  
Nonlinear Internal Waves ◽  
Leading Role ◽  
Bottom Boundary Layers ◽  
Shelf Region

AbstractThe inner shelf is a region inshore of that part of the shelf that roughly obeys Ekman dynamics and offshore of the surf zone. Importantly, this is where surface and bottom boundary layers are in close proximity, overlap, and interact. The internal tide carries a substantial amount of energy into the inner shelf region were it eventually dissipates and contributes to mixing. A part of this energy transformation is due to a complex interaction with the bottom, where distinctions between nonlinear internal waves of depression and elevation are blurred, indeed, where polarity reversals of incoming waves take place. From an intensive set of measurements over the inner shelf off central California, we identify salient differences between onshore pulses from waves with properties of elevation waves and offshore pulses from shallowing depression waves. While the velocity structures and amplitudes of on/offshore pulses 1 m above the seafloor are not detectably different, onshore pulses are both more energetically turbulent and carry more sediments than offshore pulses. Their turbulence is also oppositely skewed: onshore pulses slightly to the leading edges, offshore pulses to the trailing edges of the pulses. We consider in turn three independent mechanisms that may contribute to the observed asymmetry: propagation in adverse pressure gradients and the resultant inflection point instability, residence time of a fluid parcel in the pulse, and turbulence suppression by stratification. The first mechanism may largely explain higher turbulence in the trailing edge of offshore pulses. The extended residence time may be responsible for the high and more uniform turbulence distribution across onshore compared to offshore pulses. Stratification does not play a leading role in turbulence modification inside of the pulses 1 m above the bed.

scholarly journals Energy transformations and dissipation of nonlinear internal waves over New Jersey's continental shelf

2010 ◽  
Vol 17 (4) ◽  
pp. 345-360 ◽  
Author(s):  
E. L. Shroyer ◽  
J. N. Moum ◽  
J. D. Nash
Keyword(s):  
Continental Shelf ◽  
Internal Waves ◽  
Turbulent Mixing ◽  
Internal Tide ◽  
Flux Divergence ◽  
Wave Interactions ◽  
Nonlinear Internal Waves ◽  
Dissipative Loss ◽  
Peak Energy

Abstract. The energetics of large amplitude, high-frequency nonlinear internal waves (NLIWs) observed over the New Jersey continental shelf are summarized from ship and mooring data acquired in August 2006. NLIW energy was typically on the order of 105 Jm−1, and the wave dissipative loss was near 50 W m−1. However, wave energies (dissipations) were ~10 (~2) times greater than these values during a particular week-long period. In general, the leading waves in a packet grew in energy across the outer shelf, reached peak values near 40 km inshore of the shelf break, and then lost energy to turbulent mixing. Wave growth was attributed to the bore-like nature of the internal tide, as wave groups that exhibited larger long-term (lasting for a few hours) displacements of the pycnocline offshore typically had greater energy inshore. For ship-observed NLIWs, the average dissipative loss over the region of decay scaled with the peak energy in waves; extending this scaling to mooring data produces estimates of NLIW dissipative loss consistent with those made using the flux divergence of wave energy. The decay time scale of the NLIWs was approximately 12 h corresponding to a length scale of 35 km (O(100) wavelengths). Imposed on these larger scale energetic trends, were short, rapid exchanges associated with wave interactions and shoaling on a localized topographic rise. Both of these events resulted in the onset of shear instabilities and large energy loss to turbulent mixing.

Turbulence in the presence of internal waves in the bottom boundary layer of the California inner shelf

2018 ◽  
Vol 68 (4-5) ◽  
pp. 627-644 ◽  
Author(s):  
Rachel M. Allen ◽  
Julian A. Simeonov ◽  
Joseph Calantoni ◽  
Mark T. Stacey ◽  
Evan A. Variano
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Bottom Boundary Layer ◽  
Inner Shelf ◽  
Bottom Boundary

scholarly journals The Lifecycle of Nonlinear Internal Waves in the Northwestern South China Sea

2019 ◽  
Vol 49 (8) ◽  
pp. 2133-2145 ◽  
Author(s):  
Jianjun Liang ◽  
Xiao-Ming Li ◽  
Jin Sha ◽  
Tong Jia ◽  
Yongzheng Ren
Keyword(s):  
South China Sea ◽  
Internal Waves ◽  
South China ◽  
Internal Tide ◽  
In Situ Measurements ◽  
Shelf Break ◽  
Undular Bore ◽  
Nonlinear Internal Waves ◽  
Seasonal Thermocline

AbstractThe life cycle of nonlinear internal waves (NIWs) to the southeast of Hainan Island in the northwestern South China Sea is investigated using synergistic satellite observations, in situ measurements, and numerical simulations. A three-dimensional, fully nonlinear and nonhydrostatic model with ultrafine resolution shows that a diurnal internal tide emanates from a sill in the Xisha Islands at approximately 215 km away from the local shelf break. The internal tide transits the deep basin toward the shelf break and reflects at the sea bottom and seasonal thermocline in the form of a wave beam. Arriving at the shelf break, the internal tide undergoes nonlinear transformation and produces an undular bore. Analyses of in situ measurements reveal that the undular bore appears as sharp depressions of the strong near-surface seasonal thermocline. The undular bore gradually evolves into an internal solitary wave train on the midshelf, which was detected by the spaceborne synthetic aperture radar. This finding has great implications for investigating NIWs in other coastal oceans where waves are controlled by remotely generated internal tides.

ON COASTAL - OPEN SEA DYNAMIC INTERACTIONS DEFINING PRODUCTIVITY AND ECOLOGY OF SHELF AND ADJACENT TO SHELF WATERS

2017 ◽  
Author(s):  
Vadim Navrotsky ◽  
Vadim Navrotsky
Keyword(s):  
Boundary Layers ◽  
Internal Waves ◽  
Stratified Medium ◽  
Shelf Zone ◽  
Small Scale ◽  
The Sea Of Japan ◽  
Bottom Boundary ◽  
Open Sea ◽  
Bottom Boundary Layers ◽  
Near Shore

It is known that considerable part of living matter in the ocean falls out of biological cycle irretrievably by way of sedimentation. It means that quasi-stationary state of oceanic ecosystems is possible only with supply of mineral and organic matter from land. That supply, which includes also contaminating matter, takes place mainly in near-shore regions, concentrates in bottom boundary layers, and is transferred to the open sea via shelves by means of horizontal and vertical mixing. Effective mixing in shelves is carried out by small-scale processes, which are considerably fed by energy of large-scale processes from out-of-shelf regions. The main objective of our paper is to identify mechanisms of energy transfer from large to small-scale motions and from open sea to near-shore areas. Our experiments and observations in the shelf zone of the Sea of Japan revealed important specific features in stratified bottom boundary layers: 1) Temporal intermittence of internal waves (IW) in near-bottom layers and their transformation into sequences of stratified boluses moving in non-stratified medium. 2) Extremely high horizontal and vertical velocities in the near-bottom layers. 3) Considerable power fluctuations caused by correlated fluctuations of near-bottom pressure and velocity. 4) Non-monotonic vertical structure of temperature and velocity leading to possibility of simultaneous existing of IW breaking and secondary generation of high-frequency IW by turbulence in layers with high curvature of velocity profiles. Taking into account satellite observations of high correlation between chlorophyll-a concentration in coastal and in out-of-shelf waters, as well as dispersion relations for different types of internal waves and results of our field experiments we suggest that interconnection of biological parameters in coastal and in open sea waters is exercised substantially by gravitational and inertial internal waves generated by tides and eddies in the region of continental slope near the shelf boundary.

The fate and impact of internal waves induced by strong shear current over a marginal ridge

2020 ◽  
Author(s):  
Peiwen Zhang ◽  
Wenjia Min
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Vertical Mixing ◽  
Internal Tide ◽  
Stratified Flow ◽  
Internal Tides ◽  
Energy Field ◽  
Nonlinear Internal Waves ◽  
Highly Nonlinear ◽  
Shear Current

<p>Internal waves with strong vertical mixing could be induced by stratified flow over seafloor obstacles. Noted that the stratified flow not only trigger internal tides, but also highly nonlinear internal waves like internal lee waves and internal solitary waves over steep topography features, and the highly nonlinear internal waves are suggested to play an important role in turbulence and mixing. As a typical seafloor obstacle, ridge could significantly modified the propagation of internal tide, internal lee wave and internal solitary wave. We focused on I-Lan ridge with asymmetrical topography feature in Kuroshio region. To the north of the I-Lan ridge, the depth of Philippine basin reached 4000m compared with the depth of 1500m in the south of the ridge, leading to different characteristics of internal wave energy field and ecological characteristics between two sides. Based on numerical simulations, we revealed the generation and propagation of internal waves over marginal ridge, causing by the shear current induced by Kuroshio. We also discussed the turbulence kinetic energy contributed by linear internal waves and nonlinear internal waves, providing the strength of vertical turbulent mixing around the I-Lan ridge. Then we demonstrated the characteristics of complex internal wave field in the strong background shear current over I-Lan ridge.</p>

Energy Transport by Nonlinear Internal Waves

2007 ◽  
Vol 37 (7) ◽  
pp. 1968-1988 ◽  
Author(s):  
J. N. Moum ◽  
J. M. Klymak ◽  
J. D. Nash ◽  
A. Perlin ◽  
W. D. Smyth
Keyword(s):  
Internal Waves ◽  
Energy Flux ◽  
Energy Transport ◽  
Internal Tide ◽  
Surface Displacement ◽  
Bottom Layer ◽  
Ekman Transport ◽  
Nonlinear Internal Waves ◽  
Advection Term ◽  
The Waves

Abstract Winter stratification on Oregon’s continental shelf often produces a near-bottom layer of dense fluid that acts as an internal waveguide upon which nonlinear internal waves propagate. Shipboard profiling and bottom lander observations capture disturbances that exhibit properties of internal solitary waves, bores, and gravity currents. Wavelike pulses are highly turbulent (instantaneous bed stresses are 1 N m−2), resuspending bottom sediments into the water column and raising them 30+ m above the seafloor. The wave cross-shelf transport of fluid often counters the time-averaged Ekman transport in the bottom boundary layer. In the nonlinear internal waves that were observed, the kinetic energy is roughly equal to the available potential energy and is O(0.1) megajoules per meter of coastline. The energy transported by these waves includes a nonlinear advection term 〈uE〉 that is negligible in linear internal waves. Unlike linear internal waves, the pressure–velocity energy flux 〈up〉 includes important contributions from nonhydrostatic effects and surface displacement. It is found that, statistically, 〈uE〉 ≃ 2〈up〉. Vertical profiles through these waves of elevation indicate that up(z) is more important in transporting energy near the seafloor while uE(z) dominates farther from the bottom. With the wave speed c estimated from weakly nonlinear wave theory, it is verified experimentally that the total energy transported by the waves is 〈up〉 + 〈uE〉 ≃ c〈E〉. The high but intermittent energy flux by the waves is, in an averaged sense, O(100) watts per meter of coastline. This is similar to independent estimates of the shoreward energy flux in the semidiurnal internal tide at the shelf break.

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

2011 ◽  
Vol 41 (7) ◽  
pp. 1345-1363 ◽  
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.

ON COASTAL - OPEN SEA DYNAMIC INTERACTIONS DEFINING PRODUCTIVITY AND ECOLOGY OF SHELF AND ADJACENT TO SHELF WATERS

2017 ◽  
Author(s):  
Vadim Navrotsky ◽  
Vadim Navrotsky
Keyword(s):  
Boundary Layers ◽  
Internal Waves ◽  
Stratified Medium ◽  
Shelf Zone ◽  
Small Scale ◽  
The Sea Of Japan ◽  
Bottom Boundary ◽  
Open Sea ◽  
Bottom Boundary Layers ◽  
Near Shore

It is known that considerable part of living matter in the ocean falls out of biological cycle irretrievably by way of sedimentation. It means that quasi-stationary state of oceanic ecosystems is possible only with supply of mineral and organic matter from land. That supply, which includes also contaminating matter, takes place mainly in near-shore regions, concentrates in bottom boundary layers, and is transferred to the open sea via shelves by means of horizontal and vertical mixing. Effective mixing in shelves is carried out by small-scale processes, which are considerably fed by energy of large-scale processes from out-of-shelf regions. The main objective of our paper is to identify mechanisms of energy transfer from large to small-scale motions and from open sea to near-shore areas. Our experiments and observations in the shelf zone of the Sea of Japan revealed important specific features in stratified bottom boundary layers: 1) Temporal intermittence of internal waves (IW) in near-bottom layers and their transformation into sequences of stratified boluses moving in non-stratified medium. 2) Extremely high horizontal and vertical velocities in the near-bottom layers. 3) Considerable power fluctuations caused by correlated fluctuations of near-bottom pressure and velocity. 4) Non-monotonic vertical structure of temperature and velocity leading to possibility of simultaneous existing of IW breaking and secondary generation of high-frequency IW by turbulence in layers with high curvature of velocity profiles. Taking into account satellite observations of high correlation between chlorophyll-a concentration in coastal and in out-of-shelf waters, as well as dispersion relations for different types of internal waves and results of our field experiments we suggest that interconnection of biological parameters in coastal and in open sea waters is exercised substantially by gravitational and inertial internal waves generated by tides and eddies in the region of continental slope near the shelf boundary.

scholarly journals Shore-Based Video Observations of Nonlinear Internal Waves across the Inner Shelf *,+

2014 ◽  
Vol 31 (3) ◽  
pp. 714-728 ◽  
Author(s):  
Sutara H. Suanda ◽  
John A. Barth ◽  
Rob A. Holman ◽  
John Stanley
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Propagation Speed ◽  
Surface Expression ◽  
Inner Shelf ◽  
Average Width ◽  
Pixel Intensity ◽  
Nonlinear Internal Waves ◽  
Video Observations

Abstract Shore-based video remote sensing is used to observe and continually monitor nonlinear internal waves propagating across the inner shelf. Month-long measurements of velocity from bottom-mounted acoustic Doppler current profilers and temperature from thermistor chains at the 10- and 20-m isobaths are combined with sea surface imagery from a suite of cameras (Argus) to provide a kinematic description of 11 borelike internal waves as they propagate across the central Oregon inner shelf. The surface expression of these waves, commonly seen by eye as alternating rough and smooth bands, are identified by increased pixel intensity in Argus imagery (average width 39 ± 6 m), caused by the convergence of internal wave-driven surface currents. These features are tracked through time and space using 2-min time exposure images and then compared to wave propagation speed and direction from in situ measurements. Internal waves are refracted by bathymetry, and the measured wave speed (~0.15 m s−1) is higher than predicted by linear theory (<0.1 m s−1). Propagating internal waves are also visible in subsampled Argus pixel time series (hourly collections of 17 min worth of 2-Hz pixel intensity from a subset of locations), thus extending the observational record to times without an in situ presence. Results from this 5-month record show that the preferred sea state for successful video observations occurs for wind speeds of 2–5 m s−1. Continued video measurements and analysis of extensive existing Argus data will allow a statistical estimate of internal wave occurrence at a variety of inner-shelf locations.

scholarly journals Complex EOF Analysis as a Method to Separate Barotropic and Baroclinic Velocity Structure in Shallow Water

2008 ◽  
Vol 25 (5) ◽  
pp. 808-821 ◽  
Author(s):  
Catherine R. Edwards ◽  
Harvey E. Seim
Keyword(s):  
Boundary Layer ◽  
Shallow Water ◽  
Internal Structure ◽  
Internal Tide ◽  
Tidal Currents ◽  
Tidal Dynamics ◽  
Bottom Boundary ◽  
Bottom Boundary Layers ◽  
Baroclinic Modes ◽  
Ceof Analysis

Abstract Defining the vertical depth average of measured currents to be barotropic is a widely used method of separating barotropic and baroclinic tidal currents in the ocean. Away from the surface and bottom boundary layers, depth-averaging measured velocity is an excellent estimate of barotropic tidal flow, and internal tidal dynamics can be well represented by the difference between the measured currents and their depth average in the vertical. However, in shallow and/or energetic tidal environments such as the shelf of the South Atlantic Bight (SAB), bottom boundary layers can occupy a significant fraction of the water column, and depth averaging through the bottom boundary layer can overestimate the barotropic current by several tens of centimeters per second near bottom. The depth-averaged current fails to capture the bottom boundary layer structure associated with the barotropic tidal signal, and the resultant estimate of baroclinic tidal currents can mimic a bottom-trapped internal tide. Complex empirical orthogonal function (CEOF) analysis is proposed as a method to retain frictional effects in the estimate of the barotropic tidal currents and allow an improved determination of the baroclinic currents. The method is applied to a midshelf region of the SAB dominated by tides and friction to quantify the effectiveness of CEOF analysis to represent internal structure underlying a strong barotropic signal in shallow water. Using examples of synthesized and measured data, EOF estimates of the barotropic and baroclinic modes of motion are compared to those made using depth averaging. The estimates of barotropic tidal motion using depth-averaging and CEOF methods produce conflicting predictions of the frequencies at which there is meaningful baroclinic variability. The CEOF method preserves the frictional boundary layer as part of the barotropic tidal current structure in the gravest mode, providing a more accurate representation of internal structure in higher modes. The application of CEOF techniques to isolate internal structure co-occurring with highly energetic tidal dynamics in shallow water is a significant test of the method. Successful separation of barotropic and baroclinic modes of motion suggests that, by fully capturing the effects of friction associated with the barotropic tide, CEOF analysis is a viable technique to facilitate examination of the internal tide in similar environments.

Sign in / Sign up

Export Citation Format

Share Document