An estimate of Lagrangian eddy statistics and diffusion in the mixed layer of the Southern Ocean
Résumé
A statistical analysis of surface drifter observations is used to compute eddy length and time scales and eddy diffusion in the Southern Ocean. Eddy diffusion values of the order of 10(4) m(2) s(-1) are found in the energetic western boundary currents north of the Antarctic Circumpolar Current (ACC) and secondary peaks occur where the ACC negotiates topography. the diffusivity shows an increase from the Antarctic continent to the core of the ACC. then a slight decrease or a stable plateau within the ACC. North of the ACC, diffusivity generally decreases into the interior of ocean basins. except ill the western boundary regions where values are maximum. Diffusivity is also calculated front simulated trajectories based on altimetric geostrophic velocities with and without mean flow, as well as with simulated trajectories based on Ekman currents. Ekman currents at the drogue depth (15 m) have only a small impact, and file geostrophic currents dominate the eddy diffusivity. Complementary statistical analyses confirm these results. the surface drifter cross-stream eddy diffusion is used to test a simple parameterization bawd oil satellite altimetric observations of eddy kinetic enemy (EKE). For EKE >= 0.015 m(2) s(-2), K = 1.35 root EKELd m(2) s(-1), where L-d is the first baroclinic Rossby radius. This parameterization holds ill the energetic ACC consistent with an eddy field ill the "frozen field" regime. Over the broader areas of weaker eddy fields. mixing is fairly uniform and stable at about K = 1800 +/- 1000 m(2) s(-1).