Internal Tides in the Strait of Gibraltar

Abstract

Analysis of moored current measurements in the Strait of Gibraltar is provided here. The vertical internal displacements (double amplitudes) with a semidiurnal frequency are extremely large and sometimes exceed 200 m. It is found that these displacements are associated with forced tidal internal waves over Camarinal Sill, which crosses the strait. The separation of tidal components showed that the amplitude of internal tide with M2 frequency is 69 m, while the amplitudes of other components of the internal tide (S2, K1, O1) are 3?5 times smaller. The amplitudes of the waves decrease with the distance from the sill and, at a distance of 50 km from the sill, the amplitudes are 3 times smaller than over the sill. The energy of internal tides is transferred to internal bore and turbulent mixing. The wavelength of the internal tide was estimated on the basis of moored measurements. The wavelength of the east-propagated wave is 90 km, while the west-propagated wave is 60 km. Numerical modeling demonstrates that the lower current in the strait directed from the Mediterranean Sea to the ocean, which occupies the major part of the water column, has a significant influence on internal tides. The effect of internal waves propagating in a hydraulic flow leads to the formation of an internal bore, followed by a wave packet of shorter internal waves. The shear formed by two opposite currents intensifies the bore and short-period internal waves in the eastern part of the strait in the upper layer.