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Ann. Geophys., 21, 323-344, 2003
www.ann-geophys.net/21/323/2003/
© European Geosciences Union 2003
A high resolution hydrodynamic 3-D model simulation of the malta shelf area
A. F. Drago1, R. Sorgente2, and A. Ribotti2
1Physical Oceanography Unit, IOI-Malta Operational Cnt., University of Malta, c/o 36, Old Mint St., Valletta, VLT 12, Malta
2CNR-IAMC, Sect. Oristano, c/o International Marine Centre, Loc. Sa Mardini, 09072 Torregrande-Oristano, Italy
Abstract. The seasonal variability
of the water masses and transport in the Malta Channel and proximity of the
Maltese Islands have been simulated by a high resolution (1.6 km horizontal
grid on average, 15 vertical sigma layers) eddy resolving primitive equation
shelf model (ROSARIO-I). The numerical simulation was run with climatological
forcing and includes thermohaline dynamics with a turbulence scheme for the
vertical mixing coefficients on the basis of the Princeton Ocean Model (POM).
The model has been coupled by one-way nesting along three lateral boundaries
(east, south and west) to an intermediate coarser resolution model (5 km)
implemented over the Sicilian Channel area. The fields at the open boundaries
and the atmospheric forcing at the air-sea interface were applied on a
repeating "perpetual" year climatological cycle.
The ability of the model to reproduce a realistic circulation
of the Sicilian-Maltese shelf area has been demonstrated. The skill of the
nesting procedure was tested by model-modelc omparisons showing that the major
features of the coarse model flow field can be reproduced by the fine model
with additional eddy space scale components. The numerical results included
upwelling, mainly in summer and early autumn, along the southern coasts of
Sicily and Malta; a strong eastward shelf surface flow along shore to Sicily,
forming part of the Atlantic Ionian Stream, with a presence throughout the year
and with significant seasonal modulation, and a westward winter intensified
flow of LIW centered at a depth of around 280 m under the shelf break to the
south of Malta. The seasonal variability in the thermohaline structure of the
domain and the associated large-scale flow structures can be related to the
current knowledge on the observed hydrography of the area. The level of
mesoscale resolution achieved by the model allowed the spatial and temporal
evolution of the changing flow patterns, triggered by internal dynamics, to be
followed in detail. This modelling effort has initiated the treatment of the
open boundary conditions problem in view of the future implementation of
shelf-scale real-time ocean forecasting through the sequential nesting of a
hierarchy of successively embedded model domains for the downscaling of the
hydrodynamics from the coarse grid Ocean General Circulation Model of the whole
Mediterranean Sea to finer grids in coastal areas.
Key words. Oceanography: general
(continental shelf processes; numerical modelling) Oceanography: physical
(general circulation)
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