CHARACTERISTICS

DESCRIPTION

Identification

OPTOS
OPTOS is based on the COHERENS model, which has been developed by an international team within the frame of various EU funded projects (MAST-0050-C [Profile I], MAS2-CT93-0054 [Profile II] and MAS3-CT97-0088 [Coherens]).
Model operator: MUMM

Scope

The model forecasts currents and sea surface elevation induced by the tide, the atmospheric pressure and the wind stress. It can also be used to predict the temperature and the salinity.

Conceptual background

COHERENS is a freely available multi-purpose three-dimensional hydrodynamic model for coastal and shelf seas resolving mesoscale to seasonal scale processes. The hydrodynamic part is coupled to biological, resuspension and contaminant models. The governing equations of the physical part express conservation of mass and momentum. These equations are numerically solved using finite differences and the mode-splitting technique on a staggered grid (Arakawa C-grid). Predictor and corrector steps are also applied to the horizontal momentum equation to insure that the depth-integrated currents obtained from the 2D and 3D mode are identical.

Inputs

To be run as already implemented, the model needs, in input,

— the bathymetry at each grid node

— a set of tidal constituents along the open boundaries

— the atmospheric pressure and the components of the
wind speed at regular time intervals (now from U.K. Met. Office forecasts)

Supplementary initial and boundary conditions and other meteorological variables are necessary to heat and salt modules.

Geographical coverage

The model is implemented on various grids.

OPTOS-NOS is the North Sea implementation, between 48.5°N and 57°N, from 4°O up to 9°E with a grid of 5' of longitude and 2.5' of latitude (about 5km *5km).

OPTOS-BCZ focuses on the Belgian coast (from 51°N to 51.9°N and 2°E to 4.2°E); the resolution is 5 / 7 ' in longitude and 2.5 / 6 ' in latitude.

The link between the domains is achieved by a classic coupling of elevation and current at the boundaries of the smaller domain.
Sigma co-ordinates are used on the vertical with a resolution of 20 layers. The possibility is also offered to use non-uniform grid sizes.

Outputs

The model can provide:

— time series (each 10 minutes on the North Sea, each 5 minutes on the Belgian coastal area) of sea surface elevation (SSE), components of the depth mean and vertical profiles of the currents (DMC and VPC), pressure and components of wind stress at selected stations

— fields of SSE, components of the DMC and VPC, pressure and components of wind stress (each hour) on the whole
domain

Validation

Present field of application

— prevention of risk of storm surges

Possible complementary use

Present limitations, future needs and possible development

Limitations: weather forecast resolution in time and space, bathymetry precision

Developments : introduction of temperature and salinity, coupling with biology, sediment re-suspension and transport parts, implementation of curvilinear co-ordinates

Need for future developments : river discharge, boundary and initial conditions for the introduction of temperature and salinity

Reference of representative publication

for more information, visit the COHERENS web site http://www.mumm.ac.be/coherens