Transport by Lagrangian Vortices in the Eastern Pacific

Abstract

Rotationally coherent Lagrangian vortices (RCLVs) are identified from satellite-derived surface geostrophic velocities in the Eastern Pacific (180${}^{\circ }$-130${}^{\circ }$ W) using the objective (frame-invariant) finite-time Lagrangian-coherent-structure detection method of Haller et al. (2016) based on the Lagrangian-averaged vorticity deviation. RCLVs are identified for 30, 90, and 270 day intervals over the entire satellite dataset, beginning in 1993. In contrast to structures identified using Eulerian eddy-tracking methods, the RCLVs maintain material coherence over the specified time intervals, making them suitable for material transport estimates. Statistics of RCLVs are compared to statistics of eddies identified from sea-surface height (SSH) by Chelton et al. 2011. RCLVs and SSH eddies are found to propagate westward at similar speeds at each latitude, consistent with the Rossby wave dispersion relation. However, RCLVs are uniformly smaller and shorter-lived than SSH eddies. A coherent eddy diffusivity is derived to quantify the contribution of RCLVs to meridional transport; it is found that RCLVs contribute less than 1% to net meridional dispersion and diffusion in this sector, implying that eddy transport of tracers is mostly due to incoherent motions, such as swirling and filamentation outside of the eddy cores, rather than coherent meridional translation of eddies themselves. These findings call into question prior estimates of coherent eddy transport based on Eulerian eddy identification methods.

References in corpus (4)

• Defining Coherent Vortices Objectively from the Vorticity
• The life cycle of a coherent Lagrangian Agulhas ring
• Polar rotation angle identifies elliptic islands in unsteady dynamical systems
• Efficient Computation of Null-Geodesic with Applications to Coherent Vortex Detection

Cited by in corpus (6)

• Quasi-Objective Coherent Structure Diagnostics from Single Trajectories
• Internal wave boluses as coherent structures in a continuously stratified fluid
• Role of Coherent Eddies in Potential Vorticity Transport in Two-layer Quasigeostrophic Turbulence
• Identification of individual coherent sets associated with flow trajectories using Coherent Structure Coloring
• Quasi-Objective Eddy Visualization from Sparse Drifter Data
• Demographics of Mesoscale Eddies in an Eddy-Permitting Ocean Model and Reanalysis