Simulation of the semidiurnal tides in the Strait of Gibraltar

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

Lattice Boltzmann Simulation for Shallow Water Flow Applications

“…As expected, the time series show two tidal periods with different amplitude and frequencies. They are in good agreement with those previously computed in Castro et al (2004); Tejedor et al (1999). Similar results not presented here, have been obtained at other locations in the Strait of Gibraltar.…”

“…Secondly, the Strait contains complex fully two-dimensional flow structures, which present a challenge in the shallow water modelling. The Strait of Gibraltar has also been the subject of numerous investigations such as water circulation, hydrodynamic processes and tides, compare Almazán et al (1988); González & Sánchez-Arcilla (1995); Lafuente et al (1990); Tejedor et al (1999) among others. In all these references, the simulation domain is restricted by the Tangier-Barbate axis from the Atlantic Ocean and the Ceuta-Algeciras axis from the Mediterranean sea, see Figure 7.…”

“…For instance, two bumps with minimum bathymetric values of 997m and 463m are localized in the vicinity of the eastern exit of the Strait and the Caraminal Sill, respectively. All simulations used a constant Manning coefficient of n b = 0.012s/m 1/3 , a Coriolis parameter of Ω = 8.55 × 10 −5 s −1 , and a typical value for the horizontal eddy viscosity of ν = 100m 2 /s known in the literature, see for example González & Sánchez-Arcilla (1995); Tejedor et al (1999). A no-slip boundary condition for velocity variables was applied to the coastal boundaries.…”

Water Circulation, Sediment Transport, and Pollutant Dynamics in Southern Iberia Waters: A Review on Numerical Modelling Studies

“…e tidal signal is so strong that it reverses the currents near the bottom for a part of each tidal cycle. As a consequence, 2D depth-averaged models have already been applied to simulate surface tides in the Strait [27]. Tsimplis et al [28] have even used a 2D barotropic model for simulating tides in the whole Mediterranean Sea.…”

Coastal Altimetry Products in the Strait of Gibraltar

“…The seasonal and interannual oscillations of these fluxes [21], [22], [23], [24] (among others) are responsible for a sea level difference observed between the Atlantic and the Mediterranean Sea that might be driven by different forcing mechanisms: tides [25], atmospheric pressure variations [26], steric contributions [27], geostrophic controls inside the strait [28] and winds in the surrounding area [29], [24], [30]. In addition to this quasi-steady two-layer water exchange a mesotidal and semidiurnal tide dynamics is observed [31], [32], [33], [34] [35]. The water flow interaction with the topography (Camarinal Sill) in the western side of the strait under certain hydrographic conditions generates a train of internal waves, which move mainly toward the Mediterranean Sea [36], [37], [38], [39], [40].…”