No abstract

No abstract

Abstract. The M 2 and S2 surface tides in the Strait of Gibraltar are simulated using a two-dimensional, nonlinear, boundary-fitted coordinate model with a nominal resolution of -0.5 km. Good agreement is achieved with tide gauge and bottom pressure observations, as well as with current measurements made during the Gibraltar Experiment. The cotidal charts and the maps of tidal current ellipse parameters, which have been constructed on the basis of the model results, reproduce all of the known features of the spatial structure of the M 2 and S2 tidal waves. These results also show that a -90 ø phase difference between tidal velocity and elevation is detected in much of the Strait of Gibraltar, thus suggesting a small mean tidal energy flux through the strait. The model results give evidence of the general direction for the M 2 and S2 net tidal energy fluxes to the west. This finding is consistent with an observed southwestern tidal phase propagation and remains qualitatively unchanged when varying the strait's geometry as well as boundary and astronomical forcings. We have already mentioned topographic funnelling, which may be responsible for a nearly 90 ø phase difference between tidal velocity and elevation. This subject merits closer attention. Topographic funnelling (a term introduced by Jay [1991]) is defined as the direct dependence of tidal characteristics on the geometry of a channel. As was stated first by Hunt [1964] and thereafter by Jay [1991] and Friedrichs and Aubrey [1994], the nature of tidal waves in strongly convergent channels with friction is fundamentally different from that of classical damped tidal co-oscillations. This means that in a channel of uniform width and depth, an incident wave produces a 90 ø phase difference between tidal velocity and elevation only when it interacts with a reflected wave of nearly equal amplitude, in contrast to a channel with an exponential change in cross-sectional area, where the same incident wave can produce an identical phase difference without the presence of a reflected wave.Jay [1991] analyzed the asymptotic cases of weak convergence (friction and changes in geometry are weak relative to the acceleration), strong convergence (friction and acceleration are weak relative to the effect of geometry), critical convergence (acceleration and geometry effects are equal and of opposite sign), and supercritical convergence (strong changes in geometry with weak friction). He showed that the phase difference in exponentially convergent channels was -0 ø just 13,541

No abstract