  The three dimensional structure, dynamics and dispersion characteristics of a
simulated upwelling filament in the Iberian upwelling system are analyzed using
Lagrangian tools. We used a realistic regional simulation of the western
Iberian shelf which is concomitant with an in-situ oceanographic campaign that
surveyed the area. We compute 3d fields of finite--size Lyapunov exponents
(FSLE) from 3d velocity fields and extract the field's ridges to study the
spatial distribution and temporal evolution of the Lagrangian Coherent
Structures (LCSs) evolving around the filament. We find that the most intense
curtain-like LCSs delimit the boundaries of the whole filamentary structure
whose general properties match well the observations. The filament interior is
characterized by small dispersion of fluid elements. Furthermore, we identify a
weak LCS separating the filament into a warmer vein and a colder filament
associated with the interaction of a mesoscale eddy with the upwelling front.
The cold upwelled water parcels move along the filament conserving their
density. The filament itself is characterized by small dispersion of fluid
elements in its interior. The comparison of LCSs with potential temperature and
salinity gradient fields shows that the outer limits of the filament coincide
with regions of large hydrographic gradients, similar to those observed,
explaining the isolation of the interior of the filament with the surrounding
waters. We conclude that the Lagrangian analysis used in this work is useful in
explaining the dynamics of cross-shore exchanges of materials between coastal
regions and the open ocean due to mesoscale processes.
