Tidal dynamics in the northern Adriatic Sea

Abstract

Tides in the northern Adriatic Sea are investigated using two distinct numerical models. First, a two‐dimensional (2‐D) finite difference model is implemented with very high horizontal resolution (556 m) to simulate the northern Adriatic. After calibration of open boundary conditions the model gives very satisfactory results: The averaged vectorial difference between observed 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 vicinity 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 velocity vectors and in which the SSE is always higher to the right of the local current. These features emphasize the rotational character that tides can exhibit in a relatively small basin. Wave fitting to the current elevation structure shows that semidiurnal tidal constituents are well represented with a system of two frictionless Kelvin waves (incident and reflected). In contrast, the diurnal constituents are best described as a topographic wave propagating across, not along, the basin, from the Croatian coast to the Italian shore. Despite this obvious disparity the semidiurnal and diurnal tides can be understood as distinct members of a single family of linear waves, which exist under the combined actions of gravity and topography.