Lagrangian drifter dispersion in the southwestern Atlantic Ocean

TL;DR

This study analyzes Lagrangian drifter dispersion in the South Atlantic, comparing observational data with numerical models to understand turbulence and submesoscale influences on dispersion.

Contribution

It introduces a scale-dependent dynamical systems approach to analyze dispersion, incorporating both observational data and numerical simulations in a complex oceanic environment.

Findings

Quasigeostrophic turbulence is compatible with data analysis.

Non-stationarity and non-homogeneity affect dispersion behavior.

Submesoscale features influence relative dispersion and energy spectrum shape.

Abstract

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, we focus our 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 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. We find that, dependently on the given observable, the quasigeostrophic turbulence scenario is overall compatible with our data analysis, with discrepancies from the expected behavior of 2D turbulent trajectories likely to be ascribed to the non stationary and non homogeneous characteristics of the flow, as well as to possible ageostrophic effects. Submesoscale features of 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. We present, also, numerical simulations of an OGCM of the South Atlantic, and discuss the comparison between experimental and model data about mesoscale dispersion.