Seasonal and regional characterization of horizontal stirring in the global ocean

TL;DR

This study uses Finite-Size Lyapunov Exponents to analyze seasonal and regional variations in horizontal stirring in the global ocean, revealing significant differences linked to seasons and oceanic regions.

Contribution

It provides a detailed regional and seasonal analysis of oceanic stirring using FSLEs, filling a gap in understanding ocean transport variability.

Findings

Horizontal stirring peaks in summer.

Stirring varies significantly between hemispheres and ocean basins.

FSLE correlates with Eulerian descriptors like EKE and vorticity.

Abstract

Recent work on Lagrangian descriptors has shown that Lyapunov Exponents can be applied to observed or simulated data to characterize the horizontal stirring and transport properties of the oceanic flow. However, a more detailed analysis of regional dependence and seasonal variability was still lacking. In this paper, we analyze the near-surface velocity field obtained from the Ocean general circulation model For the Earth Simulator (OFES) using Finite-Size Lyapunov Exponents (FSLE). We have characterized regional and seasonal variability. Our results show that horizontal stirring, as measured by FSLEs, is seasonally-varying, with maximum values in Summer time. FSLEs also strongly vary depending on the region: we have first characterized the stirring properties of Northern and Southern Hemispheres, then the main oceanic basins and currents. We have finally studied the relation between averages of FSLE and some Eulerian descriptors such as Eddy Kinetic Energy (EKE) and vorticity (w) over the different regions.