Mean flow and turbulence scaling in a tidal boundary layer

Gross, Thomas F.; Nowell, Arthur R. M.

doi:10.1016/0278-4343(83)90011-0

Cited by 153 publications

(101 citation statements)

References 13 publications

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“…An alternative method for estimating the bottom stress based on bulk parameterisation is to fit a logarithmic curve, applicable to the benthic constant stress layer, to the current profile in the water column (Gross and Nowell, 1983;Lueck and Lu, 1997). where u Ã is the friction velocity; z 0 , as already described, is the roughness length and the bottom stress, t b ¼ ru 2 Ã .…”

Section: Article In Pressmentioning

confidence: 99%

Reynolds stress observations in continental shelf seas

Howarth

Souza

2005

Deep Sea Research Part II: Topical Studies in Oceanography

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The three basic observational approaches to estimating turbulence parameters in continental shelf seas are free-fall micro-structure probes from which dissipation is inferred; fast-sample (10-20 Hz) current meters in sea-bed frames measuring turbulence intensity directly; and fast-sample O(1 Hz) high-frequency Acoustic Doppler Current Profilers (ADCPs) where Reynolds stress profiles and hence turbulence production can be estimated from the variance of the along beam data. Uncertainties are associated with each approach since turbulence is a small-scale, high-frequency phenomenon and since estimates can easily be contaminated by the presence of surface waves. This paper concentrates on the latter two approaches, particularly the ADCP method, focussing on the degree of confidence that can be placed on the estimates.Results are presented from nine experiments from six sites in the North and Irish Seas and one in the Gulf of California, involving the deployment of 0.6 and 1.2 MHz standard broadband ADCPs mounted in sea-bed frames. The sites ranged from very tidally energetic, shallow (20 m deep) to low tidal energy, deeper (110 m). The ADCPs recorded data with a variety of sample regimes, from 2 to 0.5 Hz; bin sizes ranged from 0.25 to 1 m. In two of the experiments the ADCP near-bed Reynolds stress estimates were tested against independent estimates from toroidal electro-magnetic current meters measuring the three components of current (vertical and both horizontal) at 8 Hz, deployed on a nearby frame. In all cases the correlation coefficient squared between the two sets of Reynolds stress estimates was 0.7. In a further three recent deployments, an Acoustic Doppler Velocimeter (ADV) was deployed on the bottom frame with the ADV measuring volume located within the first ADCP bin and sampling at 20 or 25 Hz. The ADV measurements also show an explained variance of about 80% and a transfer function of about 1 during periods where waves were not present.One objective of these studies was to test and improve representation of dissipation processes in two-and threedimensional numerical models, including the concept of the constant stress layer. At its very simplest, bottom stress is estimated from the depth-averaged flow via a quadratic drag law. Calculations from these measurements give values for the drag coefficient between 0.0006 and 0.0019, averaging 0.0011, smaller than the value used in most depth-averaged numerical models (0.0025). There is some evidence that the value of the drag coefficient is dependent on the tidal current speed. r

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Section: Article In Pressmentioning

confidence: 99%

Reynolds stress observations in continental shelf seas

Howarth

Souza

2005

Deep Sea Research Part II: Topical Studies in Oceanography

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“…The lid was pushed down from above, bending the smaller, flexible locking posts until they locked the lid in were calculated from velocity profiles asplace. A Neoprene rubber gasket ring, consuming an equilibrium boundary layer, as tained within a circular groove cut on a 45" by Gross and Nowell (1983), using eight angle to the surface of the lid, proved effecpoints within an estimated logarithmic (log) tive in preventing sediment leakage during layer between 1.27 and 8.2 cm above the recovery or deployment of trays. A smaller, sediment surface.…”

Section: Acknowledgmentsmentioning

confidence: 99%

The role of food patches in maintaining high deep‐sea diversity: Field experiments with hydrodynamically unbiased colonization trays

Snelgrove

Grassle

Petrecca

1992

Limnology & Oceanography

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To test whether deep‐sea macrofaunal diversity is enhanced by specialization on small‐scale food patches, we deployed colonization trays by submersible at 900‐m depth for 23 d. Trays were buried flush with the seafloor to minimize potential hydrodynamic bias. Treatments included prefrozen, natural sediment that was unenriched or enriched with either Thalassiosira sp. or Sargassum sp. Density comparisons and rarefaction analysis indicate that Thalassiosira sp. attracted high densities of several taxa of juvenile opportunists, and Sargassum sp. trays were colonized by fewer individuals of a more diverse fauna. Ambient faunal diversity was higher and densities lower than enrichment treatments, although unenriched trays did not attain ambient densities. Results suggest that juveniles, rather than adults, specialize on specific patch types, thus contributing to high deep‐sea diversity; this bottleneck may be fundamentally different from less diverse, shallow‐water macrofaunal assemblages.

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“…It can be characterized by us, the boundary shear velocity, assuming steady unidirectional flow and an absence of nearby topographic features. Calcuations of u* for field flows are often made by measuring velocity profiles in the logarithmic layer of the boundary layer (Chriss and Caldwell 1982;Gross and Nowell 1983;Gross et al 1986). If a profile is not available, however, the velocity at a single height within the logarithmic layer can be used to estimate u* less precisely:…”

Section: Field Sitementioning

confidence: 99%

“…At 15"N, f= 3.8 x 1 Oe5 s-l. If the logarithmic layer is estimated as a tenth the height of the boundary layer (following Gross et al 1986), then the log layer is at least 6 m thick for values of u* > 0.5 cm s-l. Equation 1 can be used to show that current velocities (at 6 m) of 10 cm s-l and greater are fast enough to form a log layer 6 m thick.…”

Section: Field Sitementioning

confidence: 99%

Vertical distributions of the epifauna on manganese nodules: Implications for settlement and feeding

Mullineaux

1989

Limnology & Oceanography

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Over 65% of the sessile organisms living on manganese nodules from the tropical North Pacific belong to taxa whose abundances are related to vertical position on the nodule. The nodule surface texture and boundary layer flow environment, two factors that also vary vertically, were investigated to determine whether they could account for the observed faunal distributions. The surface texture of nodules from the tropical Pacific is generally rough and knobby at the nodule base and smooth near the summit. Twenty-five taxa, including 68% of the total individuals, were found in significantly different abundances between the rough and smooth surfaces of 34 nodules. These distributions may be due to larval responses to surface texture and can account for much of the observed vertical zonation of the fauna. Boundary layer flows over nodules were characterized from laboratory flume studies and field observations. In flows at the field site, it is expected that mean boundary shear stress and horizontal flux of particles (food or larvae) will increase from the nodule base to the summit, while particle contact rate and deposition will decrease. The observations that suspension feeders persist near the nodule summit and deposit feeders concentrate near the base suggest that vertical distributions of some taxa may be determined by adult feeding requirements. Individuals of most taxa are relatively scarce at the nodule base, indicating that their larvae are not colonizing where they accumulate passively. High abundances of matlike agglutinated foraminifers (of unknown feeding type) at the nodule summit may be due to larval responses to the relatively'higher shear stresses. --

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Mean flow and turbulence scaling in a tidal boundary layer

Cited by 153 publications

References 13 publications

Reynolds stress observations in continental shelf seas

Reynolds stress observations in continental shelf seas

The role of food patches in maintaining high deep‐sea diversity: Field experiments with hydrodynamically unbiased colonization trays

Vertical distributions of the epifauna on manganese nodules: Implications for settlement and feeding

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