Relative Dispersion in the Antarctic Circumpolar Current

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Authors

Dhruv Balwada, Joseph H. LaCasce, Kevin Speer, Raffaele Ferrari

Abstract

We present an analysis of relative dispersion and associated metrics from the RAFOS float observations collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) along with a set of particles from an eddy-resolving numerical model that simulated the flow in the DIMES region. Both RAFOS floats and numerical particles show correlated motions and isotropic pair spreading at length scales smaller than 100-200km and time scales smaller than 50-100 days.
Relative dispersion and pair separation PDFs for the RAFOS floats suggest that the stirring the ACC is non-local. While, relative diffusivity, finite scale Lyapunov exponents (FSLEs) and second order structure functions indicate that the stirring might be local. However, these second set of metrics are potentially influenced by internal waves and position errors that do not lead to any cumulative dispersion at timescales longer than a few inertial periods. Thus, the cumulative relative dispersion in the ACC is most probably non-local. Model-particle relative dispersion curves, relative diffusivity, separation PDFs, and FSLEs imply that the stirring experienced by the model particles is non-local, in accordance with the relatively steep energy spectra diagnosed from the model.
At large scales the dispersion is anisotropic, with meridional dispersion behaving like random walk and zonal dispersion behaving like shear dispersion. Relative diffusivity from the RAFOS floats and model particles is a function of the separation scales, with values of approximately $O(30 m^2/s)$ at about 10km separation, and grows to about $O(1000 m^2/s)$ at 200km separations.

DOI

https://doi.org/10.31223/osf.io/mhtsb

Subjects

Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics

Keywords

Submesoscale, eddy diffusivity, isopycnal stirring, Lagrangian observations, mesoscale, ocean eddies, relative dispersion

Dates

Published: 2019-10-08 19:04

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License

GNU Lesser General Public License (LGPL) 2.1

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