M2, overtides and compound tides generation in the Strait of Messina: The response of a non-hydrostatic, finite-element ocean model

The nonlinear interactions between the main tidal constituents and geographical constraints are investigated using Fluidity-ICOM, a non-hydrostatic finite-element ocean model that was implemented in the region of the Strait of Messina (Mediterranean Sea). As a first crucial approach, the barotropic tidal dynamics was investigated and the model solution was interpreted in terms of tidal maps and spectra obtained by harmonic analysis of the sea surface elevation. The model domain is represented by an unstructured mesh with variable spatial resolution ranging from two kilometres to fifty meters, in order to resolve the shoreline in the inner part of the Strait. Amplitudes and phases of the main diurnal and semidiurnal tides were prescribed at the off-shore open boundaries. A calibration procedure was carried out with available observations in order to provide a suitable parameterization for bottom drag coefficient and horizontal viscosities. The results gave clear indication that over-harmonics and compound tides are generated in the Strait. The generation mechanism, geographical localization and intensity of these phenomena were described to provide groundwork for further model analyses that would clarify the role of shallow water tides in modifying the hydrological setup in proximity of sea straits.