Tidal currents in the Adriatic as measured by surface drifters

Abstract

Velocities of surface drifters are analyzed to study tidal currents throughout the Adriatic Sea. Spectral and harmonic analyses indicate that the M2, S2, and K1 constituents dominate. Maps of tidal characteristics show that M2 and S2 are rectilinear currents (reversing tides) aligned with the main axis of the Adriatic basin with maximum amplitude (~7 cm/s for M2 and ~4 cm/s for S2) in the northern area off the Istrian Peninsula. Near the northern coast, semidiurnal tidal currents decrease in amplitude and rotate in the counterclockwise sense. Near the Po River delta, M2 (S2) motions rotate in the counterclockwise (clockwise) sense. S2 rotation is also counterclockwise near the northeastern coast. M2 phases increase from about 130° on the eastern Croatian coast to 190° on the western Italian side. S2 phases range from 150° to 200°. In the middle and southern Adriatic, the semidiurnal tides are small (~1 cm/s). The diurnal tidal currents (K1) are strong across the basin at the levels of Monte Conero and the Gargano Peninsula with speed larger than 5 cm/s and mainly clockwise rotation, and also in coastal areas (e.g., on the Albanian shelf and close to the Otranto Channel). Phases increase from the east to the west coasts (by as much as 150°). These new results compare satisfactorily with previous observations and numerical simulations, although tidal amplitudes are under‐estimated with respect to mooring measurements. They extend for the first time the description of the Adriatic tidal currents to the entire basin based on direct velocity observations.