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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L17203, doi:10.1029/2004GL020328, 2004

Mixing structures in the Mediterranean Sea from finite-size Lyapunov exponents

Francesco d'Ovidio

Instituto Mediterráneo de Estudios Avanzados IMEDEA (CSIC-UIB), Palma de Mallorca, Spain


Vicente Fernández

Instituto Mediterráneo de Estudios Avanzados IMEDEA (CSIC-UIB), Palma de Mallorca, Spain


Emilio Hernández-García

Instituto Mediterráneo de Estudios Avanzados IMEDEA (CSIC-UIB), Palma de Mallorca, Spain


Cristóbal López

Instituto Mediterráneo de Estudios Avanzados IMEDEA (CSIC-UIB), Palma de Mallorca, Spain


Abstract

We characterize horizontal mixing and transport structures in the surface circulation of the Mediterranean Sea, as obtained from a primitive equation circulation model. We calculate the Finite Size Lyapunov Exponents (FSLEs) of the velocity data set, which give a direct measure of the local stirring. By proper election of the FSLE parameters, we focus on the mesoscale structures, locating a number of vortices embedded in an intricate network of high-stretching lines. These lines control transport in the system. At the edge of the vortices, a dense tangle of line intersections appears, identifying strong mixing. The spatial distribution of FSLEs, averaged over one year, allows to classify areas in the Mediterranean basin according by their mixing activity. The space average of FSLEs on selected geographical regions gives a measure for quantifying and comparing the mixing seasonal variability.

Received 22 April 2004; accepted 22 July 2004; published 2 September 2004.

Index Terms: 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; 3220 Mathematical Geophysics: Nonlinear dynamics; 3240 Mathematical Geophysics: Chaos; 4255 Oceanography: General: Numerical modeling; 4572 Oceanography: Physical: Upper ocean processes.

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Citation: d'Ovidio, F., V. Fernández, E. Hernández-García, and C. López (2004), Mixing structures in the Mediterranean Sea from finite-size Lyapunov exponents, Geophys. Res. Lett., 31, L17203, doi:10.1029/2004GL020328.