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1990: Vol. LXVII, No. 1

Sea Level in the Strait of Gibraltar: Tides

July 31, 2015


A network of tide gauges with eight observation recording points was in operation in the Strait of Gibraltar during the years 1984 and 1985, which made it possible to draw up detailed charts of the tides showing their refined structure. For the first order, the Strait of Gibraltar represents the nodal line of the stationary wave of the western Mediterranean, which, hypothetically, would end at the Cadiz meridian (6°17.0W). The tide is basically semi-diurnal; on average, 90% of the energy is associated with the second order and, for this, the Strait of Gibraltar tends to represent an antinode of the stationary wave, although the influence of the bottom topography and the rotation is interpreted in phase delays in the sill area (slightly progressive wave) and in increased non-linear constituents of higher orders. The radiational tide S is evaluated in the area studied and it is ascertained that it shows the same characteristics as the tides having strictly gravitational constituents, which implies that it is fundamentally co-oscillating. Order 4 displays characteristics of resonant amplification due to the existence of the free oscillation mode of the western Mediterranean basin the period of which is close to 6 hours. Of order 3 it should be stressed that M3, though small, is perfectly detectable in the area.