North Adriatic tides: observations, variational data assimilation modeling, and linear tide dynamics

Abstract

Fifteen open-sea time-series observations of tidal velocities and tidal bottom pressures for more than six months duration provide a new database for North Adriatic tides. The observations show nearly reversing tidal currents at most locations and increasing tidal-current strength near Istria. Tidal elevation amplitudes and phases respectively increase northwestward and counterclockwise, strongly for semidiurnal tides and weakly for diurnal tides. The data are used for optimal determination of boundary conditions for a linear strong-constraint variational data assimilation model and the resulting average rms difference errors for tidal elevations and currents are below 1 cm and 0.5 cm s^-1, respectively. The Q factors from the model are 14.0 for M₂ and 22.4 for K₁, but comparisons between frictional dissipation estimated from the model and from the data suggest that model dissipation values could be too high by a factor of two and Q factors too small. Model potential energy is 1.5 times kinetic energy for M₂ and 6.1 times kinetic energy for K₁. Observational and modeling results suggest that energy fluxes from Kvarner Bay are significant in the North Adriatic tidal energy balance. M₂ energy fluxes support the concept of an incident and reflected Kelvin wave in the North Adriatic with some modification. K₁ energy fluxes show a northeastward cross-basin flux near the 50 m isobath where the bathymetric slope is particularly steep, with Kelvin-wave-like structures north of the ridge and departures from Kelvin-wave structure south of the ridge.