Three mesoscale eddy detection and tracking methods: Assessment for the South China sea

Abstract

Complex topography and the Kuroshio eddy-shedding process produce active mesoscale eddy activity in the South China Sea (SCS). Three eddy detection and tracking methods, the Okubo–Weiss (O-W), vector-geometry (V-G), and winding-angle (W-A) algorithms, have been widely applied for eddy identification. This study provides a comprehensive assessment of the O-W, V-G, and W-A methods in the SCS, including their detection, statistical analysis, and tracking capabilities. The mean successful detection rates of the O-W, V-G, and W-A methods are 51.9%, 56.8%, and 61.4%, respectively. The O-W and V-G methods preferentially detect eddies with medium radii (1/2°–1°), whereas the W-A method tends to detect eddies with larger radii (>1°). The V-G method identifies an excessive number of weak (radius <1/3°) eddylike structures in the SCS, accounting for 48.2% of the total eddy number. The highest mean excessive detection rate of the V-G method biases the data on eddy number, probability, and propagation direction. With the lowest mean successful tracking rate (STR), the O-W method might not be suitable for tracking long-lived eddies in the SCS. The V-G method performs well with regard to the overtracking issue and has the lowest mean questionable tracking rate of 1.1%. Among the three methods, the W-A method tracks eddies most accurately, with the highest mean STR of 80.6%. Overall, the W-A method produces reasonable statistical eddy characteristics and eddy tracking results. Each method has advantages and disadvantages, and researchers should choose wisely according to their needs.