Investigation of the Western Mediterranean's hydrodynamics with the GHER three-dimensional primitive equation model

in Coastal and Estuarine Studies (1994), 46

A three-dimensional, non-linear, primitive equation model with turbulent closure developed at the GeoHydrodynamics and Environment Research Laboratory (GHER), University of Liège, is designed to define ... [more ▼]

A three-dimensional, non-linear, primitive equation model with turbulent closure developed at the GeoHydrodynamics and Environment Research Laboratory (GHER), University of Liège, is designed to define marine weather-like processes ranging from mesoscale tides and storm surges, to synoptic frontal and eddy structures, to macroscale slowly-varying currents characteristic of the so-called “general circulation”. The model is applied here to the study of the hydrodynamics of the western Mediterranean as both a metagnostic (i.e. system-oriented) model and a diagnostic (i.e. process-oriented) model with both models allowed to run simultaneously and interactively. Critical processes such as deep water formation and the instabilities of the Algerian Current, are studied to provide a basic understanding of the physics needed to adequately parameterize sub-grid scale processes in the basin wide metagnostic model. This general circulation model provides boundary conditions for the finer grid diagnostic studies as well as the general overview of the basin's hydrodynamics. Further improvement is achieved by concurrent use of a variational inverse model to provide initial data fields and boundary conditions for the direct model. In turn, the metagnostic model provides hydrodynamic constraints which are imposed to the variational principle to ensure an interpolation/extrapolation of data compatible with the system's hydrodynamics. Results viz (i) a diagnostic study of the Algerian Current, (ii) a metagnostic study of the seasonal variability of the western Mediterranean Sea, are presented and compared with observations and with results of simpler (quasi-geostrophic, reduced gravity, etc.) models. Possible improved hydrodynamic forecasts of seasonal and interannual variability with the 3D primitive equation model is discussed with particular attention to the forecast's sensitivity to initial and boundary conditions. [less ▲]

Stability of a FBTCS Scheme Applied to the Propagation of Shallow-Water Inertia-Gravity Waves on Various Space Grids

in Journal of Computational Physics (1993), 108(1), 94-104

The equations governing the propagation of inertia-gravity waves in geophysical fluid flows are discretized on the A, B, C, and D grids according to the classical forward-backward on time and centered on ... [more ▼]

The equations governing the propagation of inertia-gravity waves in geophysical fluid flows are discretized on the A, B, C, and D grids according to the classical forward-backward on time and centered on space (FBTCS) numerical scheme. The von Neumann stability analysis is performed and it is shown that the stability condition of the inertia-gravity waves scheme is more restrictive, at least by a factor of , than that concerning pure gravity waves, whatever the magnitude of the Coriolis parameter. Finally, the general necessary and sufficient stability condition is derived for the A, B and C grids, while, on the D grid, the stability condition has been obtained only in particular cases. [less ▲]

Applying the Meridional Streamfunction Visualization Technique to Open Ocean Domains

in Ocean Modelling (1993), 101

It is common practice to represent by streamfunction the transport field ensuing from the integration - over one horizontal coordinate - of the velocity field predicted by ocean models. This very useful ... [more ▼]

It is common practice to represent by streamfunction the transport field ensuing from the integration - over one horizontal coordinate - of the velocity field predicted by ocean models. This very useful visualization technique requires that the transport field be divergenceless. If this is not the case, it is suggested to extract the divergenceless transport field that is closest to that stemming from the model while verifying the impermeability conditions of the ocean surface and bottom. A variational approach is examined. [less ▲]

Month-to-month variability of the general circulation fields in the western Mediterranean and the Gulf of Lions

in Water Pollution Research (1993), 30

The modelling and simulation of ocean's circulation on supercomputers

in Melli, P.; Zannetti, P. (Eds.) Environmental Modelling (1992)

On the use of the sigma-coordinate system in regions of large bathymetric variations

in Journal of Marine Systems (1992), 3(4-5), 381-390

The sigma-transformation is a widely used coordinate change that maps the actual depth-varying sea onto a computational domain, the depth of which is constant. The advantages of this technique are ... [more ▼]

The sigma-transformation is a widely used coordinate change that maps the actual depth-varying sea onto a computational domain, the depth of which is constant. The advantages of this technique are numerous. It permits an efficient use of computer resources, a simple treatment of the surface and bottom boundary conditions, and an accurate representation of the bathymetry. However, if the range of the depth is too large, or when the depth varies too rapidly, as in the shelf break region, it may be shown that the sigma-transformation leads to severe numerical errors. In the application of GHER's three-dimensional model to the Western Mediterranean, the occurrence of those numerical errors is avoided by the introduction of a two-fold sigma-coordinate system in the deep sea. [less ▲]

Model of the algerian currents instability

in Journal of Marine Systems (1992), 3(4-5), 441-451

A preliminary ''small-perturbation'' analytical study of a non-dissipative idealized model of the Algerian Current is made, with the aim of identifying major characteristic scales and investigating the ... [more ▼]

A preliminary ''small-perturbation'' analytical study of a non-dissipative idealized model of the Algerian Current is made, with the aim of identifying major characteristic scales and investigating the reality of possible classical instability mechanisms. The simple configuration is shown to be stable, from a linear perturbation point of view. The GHER 3D Primitive Equation Model is then applied to a more realistic investigation of the Algerian Current. The GHER model is non-linear, three-dimensional, with turbulent closure, mode splitting and a sigma-Coordinate formulation. The numerical simulation shows the development and mature pattern of the instability in excellent agreement with the observations. The relative importance of the existence of a coastal boundary layer, the nature of the initial perturbation, baroclinic and non-linear effects on the instability mechanism is discussed. [less ▲]

Modelling the Western Mediterranean : from hydrology to hydrodynamics

in Water Pollution Research (1991), 28

Application of the GHER 3D general circulation model to the Western Mediterranean

in Journal of Marine Systems (1991), 1(4), 315-332

The GHER 3D k− OGCM is briefly described and its application to the Western Mediterranean Sea's specifities is discussed. The simulation of the Western Mediterranean General Circulation in typical winter ... [more ▼]

The GHER 3D k− OGCM is briefly described and its application to the Western Mediterranean Sea's specifities is discussed. The simulation of the Western Mediterranean General Circulation in typical winter conditions shows that the model is able to reproduce the main physical processes and the main trends of the general circulation. However, the detailed current patterns appears too sensitive to the choice of initial conditions and a better knowledge of these conditions is required for further routine forecasts. [less ▲]

Application of the GHER Model to the study of the general circulation and associated synoptical/mesoscale structures in the Western Mediterranean Sea

in Proceedings of the 32nd CIESM Congress (1990)