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| Titel |
Wind-wave and current interactions in the upper ocean |
| VerfasserIn |
Mostafa Bakhoday Paskyabi, Ilker Fer, Alastair D. Jenkins |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052458
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| Zusammenfassung |
| Observations were made of atmospheric forcing, surface waves and currents, and
temperature, salinity and current profiles in the water column using a bottom-anchored
mooring line equipped with densely-spaced oceanographic sensors and a Wavescan surface
buoy fitted with a downlooking acoustic Doppler current profiler (ADCP) and a 5-m
meteorological mast. The mooring was deployed on 16 June 2010 over the 277 m isobath on
the continental shelf west of Trondheim, mid-Norway. Two-month long time series were
recovered and analysed. The water column was strongly stratified, with the buoyancy
frequency decreasing linearly from about 11 cycles per hour (cph) to 3 cph in the upper 100
m. The depth-averaged currents were dominated by the semi-diurnal tides. Frequency spectra
of the baroclinic currents show a broad-band (between 24 and 6 h period) enhanced variance
in the clockwise rotating component with a peak at the near-inertial frequency,
suggesting that wind forcing energized the internal wave continuum. Cross-spectra
between the wind speed and upper layer currents show high correlations. A significant
peak is observed at the semidiurnal frequency in the counter-clockwise rotating
component, suggesting the presence of internal tides. A storm with wind speed of
about 20 m s-1 observed early in the deployment was associated with significant
wave heights reaching 6 m, whereas the typical wave height was 1-2 m for the
remaining of the record. The interaction of the near surface tidal current with the wind
stress, and the modified wind-generated surface wave as a sea surface response
to the atmospheric forcing are analysed. This Lagrangian surface current can be
expressed as a vector sum of a quasi-Eulerian current, the wave-induced Stokes drift,
and the tidal current. The observed wave energy spectrum is used to calculate the
Stokes drift. The quasi-Eulerian current and Stokes drift are compared with the wind
speed magnitude and direction. The contribution of the wave-induced Stokes drift
to the vertical momentum transport is calculated numerically using the General
Ocean Turbulence Model with modifications to include i) the effects of Stokes shear
production on the conventional shear production, ii) revised Coriolis terms in the
momentum equations, iii) an extra momentum source term associated with wave energy
dissipation, and iv) an altered upper boundary condition due to wave energy input. |
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