Finite Size Lyapunov Exponents and Orientations of the associated eigenvectors

Overview

The maps of Backward-in-time, Finite-Size Lyapunov Exponents (FSLEs) and Orientations of associated eigenvectors are computed over altimetrc data and over global ocean within the SALP/Cnes project in collaboration with CLS, LOcean and CTOH. These products 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 (in clear colors on the figure) 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.

Even if few studies have been done on eigenvectors associated to FSLEs, it is known that the orientation of eigenvectors are also in good agreement with the geophysical tracer gradient orientation. Moreover, it is more robust to compare angles than filaments positions. Thus this variable is proposed in the products to encourage its use in future studies.

Variables
actual advection time

Orientation of the eigenvectors associated to themaximum eigenvalues of Cauchy-Green strain tensor

effective final separation distance

FLE associated to the minimum eigenvalues of Cauchy-Green strain tensor

Orientation of the eigenvectors associated to theminimum eigenvalues of Cauchy-Green strain tensor

FLE associated to the maximum eigenvalues of Cauchy-Green strain tensor

Temporal coverage   
2016-07-16 / today – 7

Geographical coverage
exemple : Latitude = -65/85; Longitude = 0/360

Spatial resolution
exemple : 1/8 degree

Update frequency
Daily

Producer
CLS/SSALTO/Duacs

Data access
NRT (last month)