The energy of near‐surface internal waves in the strait of Georgia

Experiments are made in which a stratified shear flow, accelerating from rest and containing a level where the direction of flow reverses, is generated over a rough floor. The roughness elements consist of parallel square bars set at regular intervals normal to the direction of flow. Radiating internal gravity waves are generated in the early stages of flow, whilst flow separation behind the bars produces turbulent mixing regions which eventually amalgamate and entirely cover the floor. This turbulent layer spreads vertically less rapidly than the internal waves. Observed features of the waves are compared with those predicted by a model in which the floor is assumed to be sinusoidal, and fair agreement is found for the amplitude, phase and vertical wavenumber of the waves, even when the latter becomes large.The rate of spread of the turbulent layer depends on the separation of the bars. Some interaction between the turbulence and the internal waves occurs near the edge of the turbulent layer. Wave-breaking is prevalent and the vertical scale of the waves is affected by turbulent eddies. The radiating internal waves are suppressed by replacing the bars by an array of square cubes, but there is continued evidence of features resembling internal waves near the boundary of the turbulent region. Structures are observed which bear some similarities to those found at the foot of the near-surface mixing layer in a lake.

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Longshore Current Generation by Internal Waves in the Strait of Georgia

Canadian Journal of Earth Sciences ◽

10.1139/e75-041 ◽

1975 ◽

Vol 12 (3) ◽

pp. 472-488 ◽

Cited By ~ 3

Author(s):

Richard E. Thomson

Keyword(s):

Internal Waves ◽

Maximum Speed ◽

Longshore Current ◽

Delta Area ◽

Strait Of Georgia ◽

Wave Characteristics ◽

Fraser River Delta ◽

Vertical Eddy ◽

Measured Water ◽

A Current

Presented in this paper is a derivation of the longshore current generated by breaking lowest mode internal waves in a two layer fluid of slowly shallowing depth, with emphasis on the nearshore region of the Fraser River delta in the Strait of Georgia. It is proposed that such a current, having a maximum speed of order 104/μv cm3/s2 (equal to 102 cm/s for reasonable vertical eddy viscosities, μv, of 102 cm2/s) and a width of order kilometers based on measured water properties and internal wave characteristics in the Strait, is responsible for the persistent northward flow observed to be associated with the delta in summer. Accordingly, it is suggested that the longshore current would have important implications to sedimentation rates and pollutant dispersal in the delta area, with greatest effects possibly occurring in summer and fall when the stratification in the Strait of Georgia is most pronounced.

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A numerical investigation of solitary internal waves with trapped cores formed via shoaling

Journal of Fluid Mechanics ◽

10.1017/s002211200100636x ◽

2002 ◽

Vol 451 ◽

pp. 109-144 ◽

Cited By ~ 98

Author(s):

KEVIN G. LAMB

Keyword(s):

Internal Waves ◽

Mixed Layer ◽

Propagation Speed ◽

Horizontal Velocity ◽

Buoyancy Frequency ◽

Surface Mixed Layer ◽

Near Surface ◽

Flow Limit ◽

Wave Propagation Speed ◽

Solitary Internal Waves

The formation of solitary internal waves with trapped cores via shoaling is investigated numerically. For density fields for which the buoyancy frequency increases monotonically towards the surface, sufficiently large solitary waves break as they shoal and form solitary-like waves with trapped fluid cores. Properties of large-amplitude waves are shown to be sensitive to the near-surface stratification. For the monotonic stratifications considered, waves with open streamlines are limited in amplitude by the breaking limit (maximum horizontal velocity equals wave propagation speed). When an exponential density stratification is modified to include a thin surface mixed layer, wave amplitudes are limited by the conjugate flow limit, in which case waves become long and horizontally uniform in the centre. The maximum horizontal velocity in the limiting wave is much less than the wave's propagation speed and as a consequence, waves with trapped cores are not formed in the presence of the surface mixed layer.

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Subsurface Jets in the Northwestern Gulf of Mexico

Journal of Physical Oceanography ◽

10.1175/2009jpo4158.1 ◽

2009 ◽

Vol 39 (11) ◽

pp. 2875-2891 ◽

Cited By ~ 3

Author(s):

Peter Hamilton ◽

Antoine Badan

Keyword(s):

Velocity Profile ◽

Gulf Of Mexico ◽

Internal Waves ◽

Vertical Axis ◽

Surface Currents ◽

Profile Data ◽

Near Surface ◽

Anomalous Density ◽

Slope Topography ◽

Upper Slope

Abstract Subsurface jets, defined as having velocity maxima >40 cm s−1 at depths between 100 and 350 m, and being surrounded by much weaker near-surface currents, have been observed over the northwestern Gulf of Mexico continental slope. The observations were from an array of 14 moorings equipped with upward-looking 75-kHz ADCPs deployed at 450–500 m. A total of 10 jet events were observed in 18 ADCP years of velocity profile data, where these events were clearly not the result of downward-propagating inertial internal waves. The jets had durations from about 1 to 8 days and were usually associated with interactions between similarly sized cyclones and anticyclones over the slope or with the interaction of an eddy with upper-slope topography. The jets are associated with potential vorticity anomalies and their inferred length scales indicate that the dynamics depart from simple geostrophic balances. Observed anomalous density gradients present during the jets seem to involve the tilting of the vertical axis of the center of rotation of one or more of the interacting eddies.

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Upslope Internal-Wave Stokes Drift, and Compensating Downslope Eulerian Mean Currents, Observed above a Lakebed

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0114.1 ◽

2016 ◽

Vol 46 (6) ◽

pp. 1947-1961 ◽

Cited By ~ 7

Author(s):

Stephen M. Henderson

Keyword(s):

Boundary Layer ◽

Internal Wave ◽

Internal Waves ◽

Outer Boundary ◽

Stokes Drift ◽

Surface Velocity ◽

Intermediate Water ◽

Mean Velocity ◽

Near Surface ◽

Velocity Fluctuations

AbstractIn a small lake, where flows were dominated by internal waves with 10–32-h period, slow but persistent mean transport of water over many wave periods was examined. Acoustic Doppler profilers (ADPs) and a vertical string of temperature loggers were deployed where the lower thermocline intersected the sloping lakebed. Near (<1 m above) the bed, internal waves, coherent with a lakewide seiche, propagated upslope at ~0.023 m s−1. Near-bed wave-induced water velocity fluctuations had a standard deviation of <0.02 m s−1. Near the surface, velocity fluctuations had similar magnitude, but lateral wave propagation was unclear. Averaged over many wave periods, the near-bed Eulerian velocity flowed downslope at ~0.01 m s−1, and was roughly cancelled by an upslope internal-wave Stokes drift (estimated by assuming that weakly nonlinear waves propagated without change of form). To examine net transport, while relaxing approximations used to estimate the Stokes drift, the observed temperature range (9°–25°C) was divided into 0.5°C increments, and the depth-integrated, wave-averaged flux of water in each temperature class was calculated. The coldest (near-bed) water was slowly transported onshore, opposite the Eulerian mean velocity. Onshore flux of warm near-surface water was comparable to an Eulerian-mean flux, indicating minimal near-surface Stokes drift. Intermediate water, from the middle of the water column and the outer boundary layer, was transported offshore by an offshore Stokes drift. The downslope near-bed Eulerian mean velocity, together with intensification of mean stratification within 0.4 m of the bed, may enhance boundary layer mixing.

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Diurnal and Seasonal Variability of Near‐Surface Oxygen in the Strait of Georgia

Journal of Geophysical Research Oceans ◽

10.1029/2018jc014766 ◽

2019 ◽

Vol 124 (4) ◽

pp. 2418-2439 ◽

Cited By ~ 2

Author(s):

Chuning Wang ◽

Rich Pawlowicz ◽

Akash R. Sastri

Keyword(s):

Seasonal Variability ◽

Surface Oxygen ◽

Near Surface ◽

Strait Of Georgia

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The use of moored inverted echo sounders for monitoring meso-zooplankton and fish near the ocean surface

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f05-013 ◽

2005 ◽

Vol 62 (5) ◽

pp. 1004-1018 ◽

Cited By ~ 17

Author(s):

Mark V Trevorrow

Keyword(s):

Acoustic Scattering ◽

Near Surface ◽

Strait Of Georgia ◽

Abundance Estimates ◽

Weak Evidence ◽

Inverted Echo Sounder ◽

Ocean Station Papa ◽

And Behavior ◽

Scatterer Size ◽

Northeast Pacific Ocean

This study evaluates the effectiveness of a 200-kHz inverted echo sounder for monitoring the abundance and behavior of near-surface zooplankton and fish. Data from both oceanic and littoral environments are examined: first from an 81-day deployment at Ocean Station Papa (OSP) in the northeast Pacific Ocean during the spring of 1996, and second from an 8-day deployment in the southern Strait of Georgia in September 1998. The analysis combines calibrated backscatter intensity, echo-amplitude statistics, and acoustic-scattering models to produce estimates of mean scatterer size and abundance. The identity of the various scatterer classes is deduced from local net trawls and reference to previous studies. At the OSP site the dominant scatterers were found to be euphausiids, pteropods, and myctophid fishes, with mean lengths of 15, 1.5, and 28 mm, respectively. At the Strait of Georgia site three fish size classes were identified: juvenile herring with mean length near 10 cm, juvenile salmon with mean length of 20 cm, and there was weak evidence for an adult salmon class. Overall, the acoustically derived abundance estimates were in reasonable agreement with the local net trawls and results from previous studies. The usefulness of sustained monitoring over diurnal and seasonal time scales is demonstrated with the OSP zooplankton data.

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