This paper presents results from a circulation model for the west Africancoast. The model covers all of the southern Atlantic but has enhancedresolution along the west African coast and in particular in the Angola Basinand Gulf of Guinea. An 11 year hind cast run was performed from 1986 to 1996using synoptic forcing fields. This simulation has produced a large amount ofdata which has been analyzed and intercompared with results in the openliterature, and a validation has been carried out using current meter data fromseveral locations off the west coast of Africa.
The oceanic processes along the western coast of Africa are strongly influencedby the Equatorial current system. The Northern Equatorial Counter Current(NECC) which continues as the Guinea Current (GC) induces strong currents andupwelling along the Ivory Coast. The Benguela Current (BC) originates from thedynamically active Benguela upwelling zone and propagates Northwards along thecoast until it separates and feeds into the Southern Equatorial Current (SEC). The Equatorial undercurrents affect the characteristics of water masses alongthe west African coast, where they also feed poleward undercurrents.
Thus, to have a realistic model for the circulation along the west coast of Africa which can be integrated for many years without being influenced by poorspecification of open boundary conditions, one either has to use a rather largedomain or alternatively nest a high resolution coastal model into a large scale South Atlantic model. The approach taken here is to apply a "global"South Atlantic model with variable grid resolution which is enhanced along thewest African coast. This allows for high resolution coastal modeling studieswithout having to specify open boundary conditions for a regional model. Theopen boundaries can be moved far enough away to not influence the particularregion of interest.
In the next Section the general model setup is discussed. Thereafter a fewexamples from the model results will be shown, and finally some results from astatistical validation will be presented.
The physical model to be used is based on the Miami Isopycnic Coordinate Ocean Model (MICOM) which is an isopycnic dynamic-thermodynamic ocean generalcirculation model developed by Bleck and coworkers1,2,3,4. In thevertical, MICOM uses potential density as the coordinate. This can clearly bedone since the stratification is a monotone function of depth, thus changing todensity as a coordinate, does not involve any assumptions or simplifications. The advantage of using density surfaces as a coordinate is evident since theeddy mixing in the ocean is mainly along neutral surfaces, or approximatelysurfaces of constant density. The cross isopycnal mixing is orders of magnitudelower5 and can in most model experiments be neglected (except forlong term climate simulations). This leads to a formalism where the ocean isdivided into a number of layers each having a density which is constant in timeand increasing with depth.
