The Barotropic Tide in the Strait of Gibraltar

Abstract

The Strait of Gibraltar represents the transition between two very different tidal regimes, that in the North Atlantic where the tidal ranges exceed 2 m and that in the Mediterranean where the ranges are less than 1 m. The surface tide within the strait is principally forced by the Atlantic tide and has a strongly semidiumal character, i.e. ~96% of the pressure and ~74% of the current variability observed are contained within this band. The cotidal chart for the principal sernidiurnal constituent M₂ presents a complicated diffraction pattern within the strait. Corange lines (lines of equal amplitude) are aligned perpendicular to the axis of the strait with a >50% magnitude decrease between Atlantic and Mediterranean sides. Cotidal lines (lines of equal phase) show a southwestern propagation emanating from a point source around Tarifa, implying a ~40 min time delay between maximum elevation at the north and south shores around the longitude of Tarifa. Using simultaneous pressure and current observations, it is shown that this apparent complicated behavior of the surface tide is the manifestation of simple, first order, along- and across-strait momentum balances.