Tidal dynamics in the northern Adriatic Sea

Tides in the northern Adriatic Sea are investigated using two distinct nume rical models. First,. a two-dimensional (2-D) finite difference model is im plemented with very high horizontal resolution (556 m) to simulate the nort hern Adriatic. After calibration of open boundary conditions the model give s very satisfactory results: The averaged vectorial difference between obse rved and simulated elevations is <1.3 cm for each of the seven major tidal constituents. Next, a 3-D finite element model is applied to the entire sea in order to provide a better simulation of the tidal currents in the vicin ity of the open boundary of the first model. Results show that the northern Adriatic behaves like a narrow rotating channel in which the instantaneous sea surface elevation (SSE) contours are aligned with the depth-averaged v elocity vectors and in which the SSE is always higher to the right of the l ocal current. These features emphasize the rotational character that tides can exhibit in a relatively small basin. Wave fitting to the current elevat ion structure shows that semidiurnal tidal constituents are well represente d with a system of two frictionless Kelvin waves (incident and reflected). In contrast, the diurnal constituents are best described as a topographic w ave propagating across, not along, the basin, from the Croatian coast to th e Italian shore. Despite this obvious disparity the semidiurnal and diurnal tides can be understood as distinct members of a single family of linear w aves, which exist under the combined actions of gravity and topography.