THE EQUATORIAL UNDERCURRENT IN A 2-LAYER SHALLOW-WATER MODEL

A theoretical study of a two layer shallow water equatorial ocean mode l is presented. We explain why this model which cannot accurately repr esent the dynamics of the tropical and extratropical areas is able to create a strong equatorial undercurrent, whose dynamics can be explain ed by a nonlinear mechanism where entrainment plays a prominent role. Under the assumptions that the meridional flow is far weaker than the zonal flow and that the dissipation is negligible, a solution is obtai ned for the intensity of the equatorial undercurrent as a function of the wind stress and the entrainment, The ratio of these two quantities is shown to define areas of acceleration and decelaration of the equa torial undercurrent. The role of dissipation is also briefly examined. The results are confirmed by numerical experiments made with a two la yer model whose first layer has a prescribed depth.