FSLE - Maps of Finite Size Lyapunov Exponents and Orientations of the associated eigenvectors

Multimission altimetry-derived gridded from Ssalto/Duacs products backward-in-time Finite Size Lyapunov Exponents and Orientations of associated eigenvectors.

The maps of Backward-in-time, Finite-Size Lyapunov Exponents (FSLEs) and Orientations of associated eigenvectors provide the exponential rate of separation of particle trajectories initialized nearby and advected by altimetry velocities. FSLEs highlight the transport barriers that control the horizontal exchange of water in and out of eddy cores.

Large FSLE values identify regions where the stretching induced by altimetry-detected mesoscale velocities is strong. Large FSLE values are typically organized in convoluted lines encircling (sub-)mesoscale filaments. Ridges of FLSE are often in good agreement with filaments of biogeochemical tracers (Ocean Color, Sea Surface Temperature,...) affected by horizontal advection. The observed filaments in tracer images correspond to stable trajectories (contraction) of the flow where streching is strong. When computed using a backward-in-time advection, the FSLE also show convoluted lines encircling sub-mesoscale filaments that are often in good agreement with the main structures of biological tracers distribution.

The Delayed-Time FSLE (DT FSLE) are computed from the gridded (or Level-4) SEA LEVEL Absolute Dynamic Topography (ADT) geostrophic velocities products delivered by the Copernicus Marine Service (https://doi.org/10.48670/moi-00149). In Delayed-Time, the maps are calculated every day since 1994/04/01. They are updated every year. The near-real-time FLSE (NRT FSLE) products are based on internal gridded (or Level-4) SEA LEVEL Absolute Dynamic Topography (ADT) geostrophic velocities products, using the same corrections as in Delayed-Time. In Near-Real-Time, the maps are delivered every day, with 20 days of delay.

The products delivered are backward-in-time Finite Site Lyapunov Exponents computed as detailed in F. d'Ovidio et al., 2004. The code was developed in collaboration between LOCEAN (F. d'Ovidio) and CLS, is available under GNU General Public License. The source code is also distributed open source if you intend to apply your own parameters and/or in regional area (see full description of the method and code delivery in Resources below). To use the code, please cite : "The code used to compute Finite Size Lyapunov Exponents, was developed in collaboration between LOCEAN (F. d'Ovidio) and CLS, is available under GNU General Public License".