FSLE

What is FSLE

FSLE is an exclusive data available with the Premium Ocean-O Service. Unlike traditional data types that directly observe or predict specific variables like temperature, currents, or chlorophyll, FSLE provides insights into dynamic behaviors.  FSLE is derived from ocean currents but highlights areas where “stretching” or “convergence” occurs. To compute it, we simulate the movement of an infinite number of small floating objects (e.g., tiny balls) on the ocean's surface. This helps us determine where these objects would go—whether they follow a stable trajectory, diverge, or converge.
The animation below illustrates this process, showing an example of particle advection by surface currents. Red particles remain on the same side of the front, while black particles cross the front:

Our algorithm analyzes this behavior globally, using six months of historical geostrophic current data updated daily, to generate the image below with a 3 km resolution:

Note: FSLE is not affected by cloud cover, making it advantageous compared to SST or chlorophyll observations under cloudy conditions.

High FSLE values pinpoint areas where currents cause significant stretching. These values are typically arranged in intricate filaments. FSLE ridges often align closely with concentration of biogeochemical tracers, such as chlorophyll, plankton, and weed line.
Below is an example of a front where two water masses meet without mixing. This is the type of front that the FSLE can highlight:

Thanks to the Ocean-O WorkSpace in TZ Professional, it is easy to display FSLE and combine it with other types of data. For example,  FSLE fronts near temperature variations are often more productive, so it makes sense to display both FLSE and SST at the same time:

Chlorophyll may also be interesting to combine as FSLE fronts on the edge of plankton-rich zones are transit points for predators.
Another strong advantage of TZ Professional is to be able to display accurate bathymetry data thanks to the TZ MAPS BathyVision. When the convergence zones identified by the FSLE overlap with bathymetric drop-offs, oceanic and biological phenomena are often amplified. This creates areas of increased nutrient and organism concentration. For example, in the picture below, we can observe a strong convergence band aligning with the drop-off of the continental shelf.

In summary, the best fishing zones are often where FSLE fronts intersect with other breaks, such as temperature changes, chlorophyll concentrations, or relief changes (bathymetry).