Lagrangian Transport through an Ocean Front in the Northwestern Mediterranean Sea

Abstract

With the tools of lobe dynamics, the authors analyze the structures present in the velocity field obtained from a numerical simulation of the surface circulation in the northwestern Mediterranean Sea. In particular, focus is placed on the North Balearic Front, the westernmost part of the transition zone between saltier and fresher waters in the western Mediterranean, which is here interpreted in terms of the presence of a semipermanent "Lagrangian barrier," across which little transport occurs. Identified are relevant hyperbolic trajectories and their manifolds, and it is shown that the transport mechanism known as the turnstile, previously identified in abstract dynamical systems and simplified model flows, is also at work in this complex and realistic ocean flow. In addition, nonlinear dynamics techniques are shown to be powerful enough to identify the key geometric structures in this part of the Mediterranean. The construction also reveals the spatiotemporal routes along which this transport happens. Topological changes in that picture, which are associated with the crossing by eddies and may be interpreted as the breakdown of the front, are also observed during the simulation.

Lagrangian descriptors and the assessment of the predictive capacity of oceanic data sets

“…Lobes are water masses surrounded by a piece of a stable manifold and a piece of an unstable manifold. Close to hyperbolic points, lobes evolve forming filaments as described for instance in Mancho et al (2008). This elongating structure is observed in Fig.…”

“…This is so because stable and unstable manifolds of hyperbolic fixed points act as separatrices that divide the phase portrait into regions in which particles have different dynamical fates. To achieve this geometrical representation in time-dependent aperiodic dynamical systems, special hyperbolic trajectories have been distinguished, which have been called distinguished hyperbolic trajectories (Ide et al, 2002;Madrid and Mancho, 2009), and the stable and unstable manifolds of such trajectories have been successfully used to describe transport in geophysical flows (Mancho et al, 2008;Branicki et al, 2011;.…”

Enabling Persistent Autonomy for Underwater Gliders with Ocean Model Predictions and Terrain-Based Navigation

“…Areas of significant productivity in the coastal ocean are highly correlated with locations of significant bathymetric relief, e.g., algal blooms (Horner et al, 1997;Anderson et al, 2002;FultonBennett, 2005;Kudela et al, 2005;Sekula-Wood et al, 2009) and ocean fronts (Mancho et al, 2008;Ferrari, 2011;Zhang et al, 2013). In these areas, every path traversed by an AUV has a depth signature that is highly variable and becomes increasingly unique the longer the trajectory becomes.…”

Lagrangian structure of flows in the Chesapeake Bay: challenges and perspectives on the analysis of estuarine flows

“…Many of these Lagrangian structures were successfully identified in geophysical flows as oceanic currents, fronts and eddies (e.g. Samelson and Wiggins, 2006;Rogerson et al, 1999;Mancho et al, 2008;Lekien et al, 2005a;Olascoaga et al, 2006;Mathur et al, 2007). These evolving structures are difficult to cross for fluid particles and they can be rather persistent.…”