A Global Atlas of Coherent Lagrangian Eddies Derived from Satellite Altimetry

Tongya Liu, Zhejiang University, Hangzhou, China and Ryan Abernathey, Lamont-Doherty Earth Observatory, Palisades, NY, United States
Methods employed to identify coherent ocean eddies can be classified into Eulerian and Lagrangian frameworks. Eddy datasets based on Eulerian methods, especially the eddy census of Chelton et al. (2011), have been used in a huge range of applications, from physics to biology. However, our recent results (Abernathey and Haller, 2018; Liu et al., 2019) show that Eulerian eddies are not necessarily coherent, with the leakage ratio reaching more than 50% over the lifespan, making them unsuitable for estimates of material transport. In this study, millions of Lagrangian particles are advected by satellite-derived surface geostrophic velocities over a period of 1993-2019. Using the method of Lagrangian-averaged vorticity deviation by Haller et al. (2016), we present a global atlas of coherent Lagrangian eddies, which are material objects by construction. This open-source dataset contains not only general feature (eddy center position, equivalent radius, rotation property, etc.) of eddies with lifespan of 30-, 60-, 90-, 120-, 150-, and 180-day, but also the trajectory of particles trapped by coherent eddy boundaries over the lifetime. We present a general statistical analysis of the Lagrangian eddy dataset, focusing on eddy generation sites, size, translation speed, and lifetime. Our eddy atlas provides an additional option for oceanographers in studying the interaction between coherent eddies and other physical or biochemical processes in the earth system.