Surface mixing of the Mediterranean sea by Finite Size Lyapunov Exponent calculation

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Horizontal transport and mixing processes are central to the
understanding of the physical, chemical, and biological dynamics of the
ocean. With the constantly increasing quality of satellite instruments
and computer simulations, a challenging problem is currently to identify
the structures underlying raw data and to link such information to
relevant geophysical processes. In this work we have studied the
mesoscale mixing of the Mediterranean sea by calculating the Finite Size
Lyapunov Exponents over DIEcast simulation velocity data. The FSLE
technique allows to compute the divergence of nearby trajectories at a
given lengthscale and to extract the Lagrangian structures (like
vortices, fronts) that organize the entire flow. By defining a
FSLE-based measure of mixing, we study seasonal fluctuations in
different geographic areas and obtain a subdivision of the Mediterranean
basin in natural regions defined by their average mixing.