Further observations of the turbulent fluctuations in a tidal current

Bowden, K. F.; Fairbairn, L. A.

doi:10.1098/rsta.1952.0008

Cited by 15 publications

(2 citation statements)

References 3 publications

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“…A linear increase in vertical eddy viscosity with tidal range in well mixed conditions is consistent with A v scaling with the product of the water column depth and the tidal current speed. A linear dependence of vertical mixing on tidal current speed in well mixed environments has been deduced from field data in many studies, including the classic work done by Bowden and Fairbairn [1952a, 1952b].…”

Section: Discussionmentioning

confidence: 99%

Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge

Chant¹

2002

J.‐Geophys.‐Res.

102

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[1] On the basis of a 301 day acoustic Doppler current profiler mooring in an estuarine tidal strait the strength and structure of secondary circulation in a region of flow curvature is related to variations in tidal forcing and river discharge. During low-flow conditions the structure of secondary flow is consistent with a centrifugally forced helical flow, with bottom flow toward the inside of the bend and surface flow toward the outside of the bend. The strength of secondary flow increases linearly with tidal range and is consistent with a vertical eddy viscosity that is linearly dependent on tidal current speed. During times of high river discharge the strength of secondary flow is significantly reduced, and its vertical structure undergoes a fundamental change over the spring/neap cycle. During spring tides the classic helical flow pattern is evident, albeit weaker than during low-flow conditions. However, during neap tides a more complex two-cell structure is evident. The change between these two states occurs with a spring/neap transition in the subtidal flow, indicating that it is also accompanied by changing stratification. Simple scaling analysis suggests that during weakly stratified conditions, secondary circulation will influence stream-wise dynamics and dispersion for channels with widths on order or less than 0.1 H/C d , where H is the water column depth and C d is a quadratic bottom drag coefficient. In contrast, during highly stratified conditions, lateral excursions due to secondary flows are limited to approximately one tenth of the channel's width and are an ineffective lateral mixing agent.INDEX TERMS: 4235 Oceanography: General: Estuarine processes; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; KEYWORDS: estuarine dynamics, secondary circulation, flow curvature, dispersive processes, spring/neap variability Citation: Chant, R. J., Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge,

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Section: Discussionmentioning

confidence: 99%

Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge

Chant¹

2002

J.‐Geophys.‐Res.

102

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“…Thus it may be sometimes E=106 but it is usually estimated of the order of magnitude of the stability as 10-7. Further, TAYLOR showed that stable internal waves are possible if Ri> 1/4, where g E dU )2 [6] Assuming dUidz-1/50 or 1/100, we have the values of R. dz So at the layer where dUldz is small, mid-depths, the TAYLER criterion would suggest that stable internal waves are possible of which period T is estimated of the order of a few minutes as E=10-6. Such a wave was not observed at 3m depth but the observed period was 20 sec as the averaging time of observation was only 4 minutes.…”

Section: Periodic Fluctuationmentioning

confidence: 89%

On the Structure of Ocean Currents (II)

Nan'niti¹

1956

Pap.Met.Geophy

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The component of turbulent velocity in the direction of the mean flow has been studied for the tidal current off Cape Kan'non. The periods of the turbulent fluctuations recorded varied from several seconds up to a few minutes and these fluctuations seem to be caused by turbulence.The ratio of mean amplitude of fluctuations to the mean current was greatest at the bottom and smallest at mid-depths. The calculated values of R(t), the auto-correlation coefficients, were seldom in accord with the theoretical result as 1-R(t)oct213.

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Some observations of turbulence near the sea bed in a tidal current

Bowden

1955

Quart J Royal Meteoro Soc

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process of making direct measurements of atmospheric pressure close to the sea surface. The apparatus is contained in a freely floating buoy, flat in shape and about 6 ft in diameter. It carries two gyroscopes, to measure the inclination of the surface, an accelerometer with two integrating circuits to measure vertical displacement, and a simplified microbarograph to measure pressure. Although the apparatus will only give the large-scale pressure distribution, we expect it to give valuable information. Several complete records have already been taken, and are now being analysed.Dr. W. V. R. MALKUS : The papers of Munk and Charnock represent to me a happy step to beyond the many purely descriptive studies of waves in recent oceanographic literature. Though these descriptive studies have encouraged new experimental inquiries, they have also restricted the interpretation of waves to a non-mechanistic statistical language. This would be satisfactory if waves were completely random gas molecules, but waves have organization, waves transport momentum and energy, wave fields are basically non-isotropic and, most important, waves are intimately interrelated with the turbulent wind field which creates them. Hence to study a mechanism for driving waves (wind field given, Munk), or to study the changes in the wind field (effect of wave field given by heuristic formulae, Charnock) is indeed a step towards mechanistic interpretation. One may hope that the next step is a joint theory; wind and waves both free to achieve a jointly stable system. This will of course be a statistical stability, but in most respects far from random. 551.465Some observations of turbulence near the sea bed in a tidal currentOceanography Department, University of Liverpool SUMMARYOceanographers are interested in turbulence in the flow of water in the sea or in estuaries because of its influence on the dynamics of water movements and mixing. These processes are more usually studied by their large-scale effects, and detailed investigation of the turbulent fluctuations has been attempted less frequently in oceanography than on the model scale or in the atmosphere. This paper deals with fluctuations in the velocity components. Earlier observations were reviewed by Bowden and Proudman (1949), who also described experiments in the Mersey estuary, using the Doodson current meter, Further observations on similar lines were described by Bowden and Fairbairn (1952a). An attempt to measure the vertical fluctuations as well as the horizontal fluctuations was made by Francis, Stommel, Farmer and Parson (1953) in the Kennebec estuary, Maine.The observations described in this paper were made using an electromagnetic flow meter, a new type of instrument for this purpose. It was possible to measure the vertical component tu, as well as the longitudinal component u, of the fluctuations, and hence the correlation between them. The instrument was designed at the National Institute of Oceanography, and uses alternating current at 50 C/S, passed through a coil, to produ...

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Further observations of the turbulent fluctuations in a tidal current

Cited by 15 publications

References 3 publications

Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge

Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge

On the Structure of Ocean Currents (II)

Some observations of turbulence near the sea bed in a tidal current

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