Barotropic tides in the Bab el Mandab Strait—numerical simulations

A two-dimensional barotropic finite element model with the grid resolution varying between 0.2 and 2 km and forced by eight principle constituents (Q1, O1, P1, K1, N2, M2, S2, and K2) was used to compute tidal elevations and currents in the Bab el Mandab Strait. Good agreement is achieved with the available observations for both diurnal and semidiurnal tidal currents and diurnal elevations; however, the model performs less satisfactorily for the semidiurnal elevations mainly due to the errors between the observed and computed phases in the region where there are amphidromic points for the M2, S2, and N2 constituents in the Strait. The results indicate that the largest amplitudes of the tidal elevations and the strongest currents are present in the southern part of the Strait. Residual circulation induced by the barotropic tides is rather weak in the major part of the Strait, and its contribution to the Red Sea water transport is small. The model results also show that barotropic energy fluxes are not very large and their direction depends on the constituent. All diurnal and one semidiurnal (N2) constituent have one major source of energy, which is the flux from the Gulf of Aden, while there are two sources of energy for the M2, S2, and K2 components: one from the Gulf and another from the Red Sea. Very small energy fluxes from the Strait to the adjacent basins indicate that almost all tidal energy is dissipated within the Strait. The distribution of the rate of energy dissipation due to bottom friction implies that the major area of dissipation is located between Perim Narrows and the Assab-Mocha line.