A numerical modelling study of upwelling filaments off the NW African coast

A fine resolution (1/12° × 1/12°) primitive equation limited area model is constructed for the region off NW Africa in the eastern North Atlantic to examine the generation of cool upwelling filaments. A seasonal shift in the trade wind pattern leads to coastal upwelling and an equatorward coastal current. The filaments form at four preferred locations along the NW African coast between 25°N and 35°N, the largest filament being at Cape Ghir. The generation mechanism for the filaments is similar to the one proposed for filaments in the California current system. As a result of baroclinic instability meanders develop on the coastal current and transport cool upwelled water offshore to form the filaments. During the relaxation phase of the upwelling a cyclonic eddy is generated to the south of the Cape Ghir plateau which serves to intensify the offshore jet at this location and leads to downwelling within the filament.