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| Titel |
Large eddy simulation model for wind-driven sea circulation in coastal areas |
| VerfasserIn |
A. Petronio, F. Roman, C. Nasello, V. Armenio |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 20, no. 6 ; Nr. 20, no. 6 (2013-12-10), S.1095-1112 |
| Datensatznummer |
250086082
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| Publikation (Nr.) |
 copernicus.org/npg-20-1095-2013.pdf |
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| Zusammenfassung |
| In the present paper a state-of-the-art large eddy simulation model
(LES-COAST), suited for the analysis of water circulation and mixing in
closed or semi-closed areas, is presented and applied to the study of the
hydrodynamic characteristics of the Muggia bay, the industrial harbor of the
city of Trieste, Italy. The model solves the non-hydrostatic, unsteady
Navier–Stokes equations, under the Boussinesq approximation for temperature
and salinity buoyancy effects, using a novel, two-eddy viscosity Smagorinsky
model for the closure of the subgrid-scale momentum fluxes. The model
employs: a simple and effective technique to take into account wind-stress
inhomogeneity related to the blocking effect of emerged structures, which, in
turn, can drive local-scale, short-term pollutant dispersion; a new nesting
procedure to reconstruct instantaneous, turbulent velocity components,
temperature and salinity at the open boundaries of the domain using data
coming from large-scale circulation models (LCM). Validation tests have shown
that the model reproduces field measurement satisfactorily. The analysis of
water circulation and mixing in the Muggia bay has been carried out under
three typical breeze conditions. Water circulation has been shown to behave
as in typical semi-closed basins, with an upper layer moving along the wind
direction (apart from the anti-cyclonic veering associated with the Coriolis
force) and a bottom layer, thicker and slower than the upper one, moving
along the opposite direction. The study has shown that water vertical mixing
in the bay is inhibited by a large level of stable stratification, mainly
associated with vertical variation in salinity and, to a minor extent, with
temperature variation along the water column. More intense mixing, quantified
by sub-critical values of the gradient Richardson number, is present in
near-coastal regions where upwelling/downwelling phenomena occur. The
analysis of instantaneous fields has detected the presence of large
cross-sectional eddies spanning the whole water column and contributing to
vertical mixing, associated with the presence of sub-surface horizontal
turbulent structures. Analysis of water renewal within the bay shows that,
under the typical breeze regimes considered in the study, the residence time
of water in the bay is of the order of a few days. Finally, vertical eddy
viscosity has been calculated and shown to vary by a couple of orders of
magnitude along the water column, with larger values near the bottom surface
where density stratification is smaller. |
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