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| Titel |
Effect of variable winds on current structure and Reynolds stresses in a tidal flow: analysis of experimental data in the eastern English Channel |
| VerfasserIn |
K. A. Korotenko, A. V. Sentchev, F. G. Schmitt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 8, no. 6 ; Nr. 8, no. 6 (2012-11-27), S.1025-1040 |
| Datensatznummer |
250006015
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| Publikation (Nr.) |
 copernicus.org/os-8-1025-2012.pdf |
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| Zusammenfassung |
| Wind and wave effects on tidal current structure and turbulence throughout
the water column are examined using an upward-looking acoustic Doppler
current profiler (ADCP). The instrument has been deployed on the seafloor of
18-m mean depth, off the north-eastern French coast in the eastern English
Channel, over 12 tidal cycles, and covered the period of the transition from
mean spring to neap tide, and forcing regimes varied from calm to moderate
storm conditions. During storms, we observed gusty winds with magnitudes
reaching 15 m s−1 and wave heights reaching up to 1.3 m. Analysis of
velocity spectra revealed a noticeable contribution of wind-induced waves to
spectral structure of velocity fluctuations within the subsurface layer.
Near the surface, stormy winds and waves produced a significant
intensification of velocity fluctuations, particularly when the sustained
wind blew against the ebb tide flow. As during wavy periods, the
variance-derived Reynolds stress estimates might include a wave-induced
contamination, we applied the Variance Fit method to obtain unbiased
stresses and other turbulent quantities. Over calm periods, the turbulent
quantities usually decreased with height above the seabed. The stresses were
found to vary regularly with the predominantly semidiurnal tidal flow. The
along-shore stress being generally greater during the flood flow
(~2.7 Pa) than during the ebb flow (~−0.6 Pa).
The turbulent kinetic energy production rate, P, and eddy viscosity,
Az, followed a nearly regular cycle with close to a quarter-diurnal
period. As for the stresses, near the seabed, we found the maximum values of
estimated quantities of P and Az to be 0.1 Wm−3
and 0.5 m2 s−1, respectively, during the flood flow. Over the storm
periods, we found the highest unbiased stress values (~−2.6 Pa) during ebb when tidal currents were opposite to the southwesterly winds
while, during the flood, the surface stresses slightly exceeded those
estimated for a calm period. A comparison of obtained results gives a good
agreement with those of other researchers working on direct measurements of
turbulence in tidal flows. |
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