TIDAL CURRENTS IN THE WESTERN MEDITERRANEAN-SEA

A large number of several-month current time series is now available i n the western Mediterranean Sea, and harmonic and spectral analyses pr ovide spatially coherent information about the major tidal (M2, S2, N2 and K1) currents in the region. When they are significant, these curr ents are generally barotropic, they mainly rotate clockwise and their ellipses have orientations that are strongly dependent on the local ba thymetry. From the Alboran Sea to the Algerian Basin, the Ibiza Channe l and as far as the Sardinian Channel, the velocities of the semidiurn al components continuously decrease from a few 10(-2) m/s in the west to 10(-3) m/s and even less in the east. The phases increase eastward from the Alboran Sea to 3-4 degrees E in the western Algerian Basin, a nd can then be considered as constant as far as similar to 9 degrees E in the Sardinian Channel. Such a phase variation is consistent with n umerical models and results from the presence of an amphidromic zone n ear 0-2 degrees E. Eastward of similar to 9 degrees E, the phases shou ld increase again, under the influence of another amphidromic zone loc ated in the Sicily Channel. In both the Gulf of Lions and the Ligurian Sea, the velocities are extremely low and the ellipse characteristics are erratic, again in agreement with the models. In the Corsican Chan nel, where relatively shallow depths induce an increase of barotropic currents, the semi-diurnal components have a phase roughly opposed to that in the southwestern part of the sea. Considering the amphidromic zone in the Sicily Channel, this out-of-phase relationship is consiste nt with the occurrence of a zone of maximum elevation in the eastern T yrrhenian Sea. The K1 currents in the Corsican Channel are lower than the M2 ones, but much larger than any other tidal current. They are ex actly in phase with the elevation in the whole sea. All these results also prove that low tidal currents can be discerned in records made by simple instruments.