A three‐dimensional eddy census of a high‐resolution global ocean simulation

Abstract

[1] A three-dimensional eddy census data set was obtained from a global ocean simulation with one-tenth degree resolution and a duration of 7 years. The census includes 6.7 million eddies in daily data, which comprise 152,000 eddies tracked over their lifetimes, using a minimum lifetime cutoff of 28 days. Variables of interest include eddy diameter, thickness (vertical extent), minimum and maximum depth, location, rotational direction, lifetime, and translational speed. Distributions of these traits show a predominance of small, thin, short-lived, and slow eddies. Still, a significant number of eddies possess traits at the opposite extreme; thousands of eddies larger than 200 km in diameter appeared in daily data each year. A tracking algorithm found hundreds of eddies with lifetimes longer than 200 days. A third of the eddies are at least 1000 m tall and many penetrate the full depth of the water column. The Antarctic Circumpolar Current contains the thickest and highest density of eddies. Thick eddies are also common in the Gulf Stream, Kuroshio Current, and Agulhas ring pathway. The great majority of eddies extend all the way to the surface, confirming that eddy censuses from surface observations are a good proxy for the full-depth ocean. Correlations between variables show that larger-diameter eddies tend to be thicker and longer lived than small eddies.

Statistical Characteristics of Mesoscale Eddies in the North Pacific Derived from Satellite Altimetry

“…Petersen et al [7] indicated that 97% of eddies with a minimum lifespan of 4 weeks extended to the surface, thus most mesoscale eddies could be detected from the sea surface. Detectability of the eddy detection algorithm is strongly affected by the spatial and temporal resolutions of satellite data.…”

“…The mesoscale eddies of long lifespans enhance mixing in the upper ocean [5,6]. Petersen et al [7] applied a numerical model to investigate the three-dimensional structure of eddies in the global oceans and indicated that approximately one-third of eddies extended to at least 1000 m in depth. Meanwhile, 97% of eddies with a minimum lifespan of 4 weeks extend to the surface, so that it is feasible to detect eddies from the sea surface.…”

Enhancing the accuracy of automatic eddy detection and the capability of recognizing the multi-core structures from maps of sea level anomaly

“…First, it is difficult to decide on the optimal or appropriate threshold value of the parameter W that makes identification more accurate (Chelton et al, 2011). Recent studies (Williams et al, 2011;Petersen et al, 2013) have developed a new R 2 algorithm to eliminate the dependency on threshold choosing, which judges the quality of an eddy based on the similarity of certain functional fits with an idealized Gaussian vortex. Second, the derivation of this physical parameter may bring extra noise that increases falsely detected eddies (Ari Sadarjoen and Post, 2000;Chaigneau et al, 2008;Chelton et al, 2011;Nencioli et al, 2010).…”

Technical Note: Watershed strategy for oceanic mesoscale eddy splitting

“…In general, the automated eddy detection algorithms are categorized into three types: (1) physical parameter-based algorithms, e.g. Okubo-Weiss (Isern-Fontanet et al, 2003;Chaigneau et al, 2008); (2) flow geometry-based algorithms (Fang and Morrow, 2003;Chaigneau et al, 2011;Petersen et al, 2013;Chelton et al, 2011;Xu et al, 2011;Wang et al, 2015); and (3) hybrid methods, which involve physical parameters and flow geometry characteristics (Nencioli et al, 2010, Xiu et al, 2010Dong et al, 2011;Yi et al, 2014). However, each identification method poses a multinuclear eddy identification problem, e.g.…”