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| Titel |
Mixing dynamics within a turbid bottom boundary layer |
| VerfasserIn |
I. Bastida, J. Planella, E. Roget |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023038
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| Zusammenfassung |
| Mixing dynamics within a turbid bottom boundary layer in a littoral zone of the
Mediterranean Sea is analyzed. Data were taken in June 2004 with a free falling
microstructure profiler. Mesoscale dynamics in the region was influenced by the outflow of
the Ebre River and by the southwestern Catalan Current originating in the Gulf of Genoa. The
magnitude of the near bottom current was 5-8 cm/s and the flow was affected by inertial
oscillations. During the entire field campaign, the wind of ~ 6 m/s was from the
northeast. The mean depth of the upper mixed layer was about 15 m, the thermocline
occupied the depth range between 15 and 30 m, and the thickness of the turbid bottom
boundary layer varied from 8 to 12 m. Different stations ranged from 15 to 60 m
depth.
Thorpe displacement, Th, was used to determine the turbulent patches and, in
general, Thmax within the patches and the Thorpe scale, LTh, were found to be highly
correlated and linearly dependent: Tmax= 2.6LTh. If Thmax and LTh were calculated at
equidistant segments of the profiles, then Thmax ~ LTh0.85. Within the bottom layer
turbulent patches were found to affect 35% of the total depth of the layer. The median
size of the patches was 41 cm and their median buoyancy Reynolds number was
252.
State of the turbulence within the bottom layer is discussed based on the turbulent
Reynolds and the turbulent Froude numbers. According to the hydrodynamic diagram and the
vertical profiles of the turbulent kinetic energy dissipation rate, different zones are identified,
including an upper interface where Kelvin-Helmholtz instability develop. The different
station-dependent structure of the turbidity profiles is related to the different mixing
dynamics. Mean turbulent diffusivity of the turbid layer was obtained following the Osborn
approach and found to be 2 x 10-5 m2/s. |
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