Lagrangian Drifter Dispersion in the Southwestern Atlantic Ocean

Stefano Berti (1, 2) , Francisco Alves dos Santos (3) , Guglielmo Lacorata (4) , Angelo Vulpiani (5, 6)

1 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]
2 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
3 PROOCEANO Serv Oceanog, Rio De Janeiro, Brazil
4 ISAC - Istituto di Scienze dell'Atmosfera e del Clima [Lecce]
5 Univ Roma La Sapienza, Dept Phys, CNR ISC, I-00185 Rome, Italy
6 Univ Roma La Sapienza, Ist Nazl Fis Nucl, Rome, Italy

In the framework of Monitoring by Ocean Drifters (MONDO) project, a set of Lagrangian drifters were released in proximity of the Brazil Current, the western branch of the subtropical gyre in the South Atlantic Ocean. The experimental strategy of deploying part of the buoys in clusters offers the opportunity to examine relative dispersion on a wide range of scales. Adopting a dynamical systems approach, the authors focus their attention on scale-dependent indicators, like the finite-scale Lyapunov exponent (FSLE) and the finite-scale (mean square) relative velocity (FSRV) between two drifters as a function of their separation and compare them with classic time-dependent statistical quantities like the mean-square relative displacement between two drifters and the effective diffusivity as functions of the time lag from the release. The authors find that, dependently on the given observable, the quasigeostrophic turbulence scenario is overall compatible with their data analysis, with discrepancies from the expected behavior of 2D turbulent trajectories likely to be ascribed to the nonstationary and nonhomogeneous characteristics of the flow, as well as to possible ageostrophic effects. Submesoscale features of similar to O(1) km are considered to play a role, to some extent, in determining the properties of relative dispersion as well as the shape of the energy spectrum. The authors also present numerical simulations of an ocean general circulation model (OGCM) of the South Atlantic and discuss the comparison between experimental and model data about mesoscale dispersion.

Domains: Ocean, Atmosphere; Oceanography

Stefano Berti, Francisco Alves dos Santos, Guglielmo Lacorata, Angelo Vulpiani. Lagrangian Drifter Dispersion in the Southwestern Atlantic Ocean. Journal of Physical Oceanography, 2011, 41 (9), pp.1659-1672. ⟨10.1175/2011jpo4541.1⟩. ⟨hal-01119197⟩