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Section: New Results

Defining coherent vortices from particles trajectories

Participants : A. El Aouni , H. Yahia , K. Daoudi , K. Minaoui .

Tracer patterns in the ocean, such as sea surface temperature, chlorophyll concentration and salinity suggest the emergence of coherence even in the ocean, typically with fluxes dominated by advective transport over diffusion. Mesoscale eddies are known to govern advective transport in the ocean, with typical horizontal scales $𝒪\left(100km\right)$ and timescales of $𝒪\left(weeks\right)$. These oceanic structures are omnipresent in the ocean and usually exhibit different properties to their surroundings. They are known to stir and mix surroundings water masses as well as by their ability to trap and carry fluid properties in a coherent manner. As the effect of these mesoscale eddies on the global circulation is remarkable, we focused on studying and understanding the dynamic transport properties of these coherent oceanic structures. For this reason, we have developed a Lagrangian method to identify and extract Lagrangian coherent vortices. The method analyzes particles' trajectories to identify vortices' boundaries and their attractor centers. Indeed, it is based on a decomposition of particle trajectory into two parts: closed curves which give information about uniformly rotating flow, and one that describes the mean displacement. The former part yields an objective measure of material rotation. We define Lagrangian coherent vortex as closed material lines in which fluid parcels complete the same polar rotation. This turns out to be filled with outward-increasing closed contours of the Lagrangian Averaged Closed Curve Length.

Publications: 3 articles submitted.