Automatic Identification of Oceanic Multieddy Structures From Satellite Altimeter Datasets

Very few of current eddy detection algorithms are capable of identifying multieddy structures resulted from interactions among eddies. In this study, we improve our previous hybrid detection (HD) algorithm by incorporating a new criterion to better identify multieddy structures from satellite altimeter data. The criterion defines an aspect ratio to determine if eddies have vortex overlaps and, as such, result in a composite structure of multiple eddies (a.k.a. multieddy structures). Compared with two previous studies on observed eddy-eddy interactions in eddy mergers from altimeter data, the improved HD algorithm not only successfully captures multieddy structures but also shows how eddies interact and evolve, including merging, splitting, and partial vorticity exchange. Tests of the improved HD algorithm on a series of sea-level anomaly maps in the South China Sea (SCS) from 1993 to 2012 show that single eddies, in contrast to eddies with composite structures, appear more concentrated in northwest of the Luzon and southeast of Vietnam. Tracking dual-eddy structures reveals several processes of eddy interactions in the SCS. The study demonstrates the potential value of the new HD algorithm in helping scientists to investigate characteristics of eddy-eddy interactions from satellite observations.