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| The velocity field of a two-dimensional fluid flow defines a two-dimensional non-autonomous dynamical system for fluid particle motion. Coherent Lagrangian (i.e., material) vortices are generalized elliptic regions in this dynamical system. Haller and Beron-Vera have recently derived an objective variational principle for such coherent vortices, obtaining their boundaries as closed material lines with infinitesimally uniform stretching. The fluid in the interior of such a curve is transported by the flow without substantial deformation.
Here, we discuss an automated detection method for such coherent vortex boundaries in spatially extended data sets. Our algorithm utilizes topological constraints on the singularities of the Cauchy-Green strain tensor field associated with the flow map. We demonstrate our algorithm by identifying coherent Lagrangian eddies in the Southern Ocean State Estimate (SOSE) data set. |
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