How reliable are finite-size Lyapunov exponents for the assessment of ocean dynamics?

Much of atmospheric and oceanic transport is associated with coherent structures. Lagrangian methods are emerging as optimal tools for their identification and analysis. An important Lagrangian technique which is starting to be widely used in oceanography is that of finite-size Lyapunov exponents (FSLEs). Despite this growing relevance there are still many open questions concerning the reliability of the FSLEs in order to analyse the ocean dynamics. In particular, it is still unclear how robust they are when confronted with real data. In this paper we analyze the effect on this Lagrangian technique of the two most important effects when facing real data, namely noise and dynamics of unsolved scales. Our results, using as a benchmark data from a primitive numerical model of the Mediterranean Sea, show that even when some dynamics is missed the FSLEs results still give an accurate picture of the oceanic transport properties.

Research highlights
► FSLEs are appropriate to study ocean at sub- and meso- scales.
► FSLEs are multifractal.
► FSLEs are robust against data-resolution transformations.
► FSLEs are robust against uncertainties in velocity data.
► FSLEs are robust against noise in particle trajectories.