Published on May 26, 2014 - By: Vincent Rossi, IFISC - Date: 2013-07-10 12:00:00 - Description: Although the Eulerian and Lagrangian descriptions of fluid motion are theoretically equivalent, this talk suggests that the latter has many advantages when investigating the ocean circulation. In the first example, I will present a novel Lagrangian methodology which identifies optimally coherent structures (Agulhas Rings) within a time varying simulated velocity field in the South Atlantic Ocean. This technique allows extracting the 3D shape of a ring, tracking its evolution over space and time while accurately measuring the amount of water remaining in the structure. We demonstrate that our method detects structures that are more coherent over time than the 3D eddies obtained from classical Eulerian techniques. In another example, I use Lagrangian trajectories to estimate the future long-term pathways of the radioactive water accidentally released in the North Pacific Ocean following the March 2011 Fukushima disaster. With a half-life of 30.1 years, Cesium-137 has the potential to travel large distances within the ocean. Based on an ensemble of eddy-resolving simulations, our results suggest that the contaminated plume would have been rapidly diluted by July 2011. The differential intrusion of the plume over the northwestern American shelves in 2014-2017 can be explained by both local and basin-scale processes. Fukushima-derived Cs-137 will penetrate the interior ocean and spread to other oceanic basins over the next three decades. Discussing the sensitivity of our results to uncertainties in the source function, the advantages of the Lagrangian approach are evidenced.
Posted on: Mon, 29 Sep 2014 04:43:24 +0000
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