Mean surface circulation and mesoscale turbulent flow characteristics in the eastern South Pacific from satellite tracked drifters
Résumé
Circulation of the eastern South Pacific region (10°-34°S, 70°-100°W) was studied using drifting buoy trajectories from 1979 to 2003. Three different current regimes were highlighted: the South Equatorial Current, flowing westward north of 26°S with surface velocities of 7-8 cm s−1; the South Pacific Current, an eastward current of ∼2 cm s−1 south of 25°-30°S; and the Chile-Peru Current, a northwestward flow of ∼6 cm s−1 found to the east of 82°W and south of 22°S. The velocity variance distribution showed the regional flow to be anisotropic in nature. Maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns, with higher energy levels near the South American coast. The Lagrangian time and length scales of the turbulent flow revealed typical values of 5.9 ± 0.6 days and 40.7 ± 5.4 km in the zonal direction and of 3.5 ± 0.4 days and 29 ± 3.4 km in the meridional direction. The estimated diffusivities were (4.9 ± 0.5) × 107 cm2 s−1 and (2.6 ± 0.3) × 107 cm2 s−1 in the eastward and northward directions, respectively. Finally, we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets. Near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large-scale circulation; mean horizontal heat and salt diffusive fluxes were around 25 W m−2 and 50 g m−2 d−1.
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