Abstract
Absolute and relative dispersion are fundamental quantities employed in order to assess the mixing strength of a basin. There exists a time scale called Lagrangian Integral Scale associated to absolute dispersion that highlights the occurrence of the transition from a quadratic dependence on time to a linear dependence on time. Such a time scale is commonly adopted as an indicator of the duration needed to lose the influence of the initial conditions. This work aims to show that in a semi-enclosed basin the choice of the formulation in order to calculate the absolute dispersion can lead to different results. Moreover, the influence of initial conditions can persist beyond the Lagrangian Integral Scale. Such an influence can be appreciated by evaluating absolute and relative dispersion recursively by changing the initial conditions. Furthermore, finite-size Lyapunov exponents characterize the different regimes of the basin.
Highlights
The Gulf of Trieste is a shallow semi-enclosed basin in the NE Adriatic Sea with a maximum depth of 25 m
We aim to evaluate such statistics varying the initial conditions, i.e. the time instance at which numerical particles are released and, the velocity at which they are subjected at the beginning of their trajectory
The absolute dispersion is strongly related to the Lagrangian time scales as shown in Eq 2
Summary
The Gulf of Trieste is a shallow semi-enclosed basin in the NE Adriatic Sea (see Fig 1) with a maximum depth of 25 m. Tidal oscillations enter in the Adriatic Sea from the Otranto strait [3]: the dominant tides are diurnal and semidiurnal. Tidal currents can enhance horizontal dispersion [4] and their footprints should be clearly identifiable in Lagrangian statistics. The aim of this work is to detect such footprints and to verify which formulation is best suited in order to evaluate absolute dispersion. Absolute dispersion measures the spread of tracers released in a water body. The behaviour of absolute dispersion is intrinsically related to the Lagrangian Integral Time TL, i.e. the integral of the auto-correlation function of residual velocities. This time defines the occurrence of the change in the slope of the absolute
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