Relative dispersion from a high-resolution coastal model of the Adriatic Sea

Synthetic drifter trajectories computed from velocity data produced by a high-resolution NCOM model are used to investigate the scaling of relative dispersion and the distribution of finite-scale Lyapunov exponent (FSLE) fields in the Adriatic Sea. The effects of varying degrees of spatial and temporal filtering of the input Eulerian velocity fields on the Lagrangian statistics are investigated in order to assess the sensitivity of such statistics to model error. It is shown that the relative dispersion in the model Adriatic circulation is generally super-diffusive, scaling nearly ballistically in close agreement with Lagrangian observations from a limited set of drifters. The large-scale dispersion is dominated by persistent separation regions and the controlling influence of the Western Adriatic Current (WAC). Temporal filtering with averaging windows up to monthly time scales only affects the relative dispersion at scales smaller than 20 km without altering the overall scaling regime. In contrast, spatial smoothing at scales as small as 5 km significantly reduces relative dispersion at all scales up to 100 km. While basin-scale dispersion statistics are strongly dependent on spatial resolution of the model WAC, maps of FSLE fields over initial conditions indicate that the detailed geometry of the dispersion is determined to a large extent by the temporal resolution of the model. In addition, the degree of spatial heterogeneity in the flow field implies that the existence, or non-existence, of a distinct exponential regime in the FSLE at small scales is extremely sensitive to the details of particle pair sampling strategies.