The surface transport in the Northeastern Adriatic Sea has been investigated by evaluating, for the first time, the Finite-Size Lyapunov Exponent (FSLE) on the current field detected by the High Frequency (HF) coastal radar network active in the period August 2007 - August 2008. A similar analysis has been carried out on the MITgcm (Massachusetts Institute of Technology general circulation model) current field in order to have a perspective on the various results given by the application of the same FSLE evaluation procedure to different velocity fields. This work includes also the development, testing and calibration of the FSLE evaluation algorithm for the specific Adriatic area considered. The aim of this thesis is to study the surface dynamics of the Northeastern Adriatic current field associated with the typical wind regimes, namely Bora and Sirocco.
The strongest and most persistent wind events, coinciding with the radar network activity, have been identified in the first instance from ALADIN (Aire Limitée Adaptation dynamique Développement InterNational) model meteorological data and then confirmed by the in situ meteo-mareographic time series in Trieste and Venice. For comparison purposes, the transport structures developing throughout the longest calm wind periods have also been investigated.
In this thesis, the combination of the FSLE resulting from model and radar current fields contributes to interpret the surface transport dynamics in the studied area. In fact, it allows: i) to determine the strongest dynamical features, ii) to extend the transport information beyond the radar coverage and iii) to bring to the light the possible ambiguity of some structures originated from model currents. The FSLE analysis evidenced along the northern Adriatic margin an attractive transport structure with a filament-shaped conformation. The dynamics of this structure is driven by the water exchange between the Gulf of Trieste (GoT) and the North Adriatic Sea. The spatial location of this filament and the advective direction associated with it, vary according to the wind patterns. In fact, in calm wind periods this attractive filament is found right in front of the gulf entrance indicating the pattern of the GoT outflow (east-west direction). During Bora episodes this attractive filament is advected westward and it elongates following the northern Adriatic coast. Differently, Sirocco wind pushes this filament closer to the northeastern coastline reversing the transport direction along it (from west to east). Previous studies evidenced that the current signal in the southern part of the domain is less correlated to the wind pattern with respect to what observed in the northern area of the current field. Therefore also from the FSLE analysis no recurrent transport dynamics is observed in the southern area except for the Bora cases, when a repulsive structure originates from the Istrian coast and it looses strength while it is advected northwestward.
