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

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  • 1 MLR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou, China
  • 2 State Key Laboratory of Tropical Oceanography (LTO), South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China
  • 3 University of Chinese Academy of Sciences, Beijing, China
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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 (SDRs) 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°), while the W-A method is tend to be larger radii (>1°). The V-G method identifies an excessive number of weak (radius<1/3°) eddy-like structures in the SCS, accounting for 48.2% of the total eddy number. The highest mean excessive detection rate (EDR) 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 regarding the over-tracking issue and has the lowest mean questionable tracking rate (QTR) 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.

Corresponding Author: Yikai Yang, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academic of Sciences, Guangzhou, China. Email: yangyikai@scsio.ac.cn

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 (SDRs) 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°), while the W-A method is tend to be larger radii (>1°). The V-G method identifies an excessive number of weak (radius<1/3°) eddy-like structures in the SCS, accounting for 48.2% of the total eddy number. The highest mean excessive detection rate (EDR) 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 regarding the over-tracking issue and has the lowest mean questionable tracking rate (QTR) 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.

Corresponding Author: Yikai Yang, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academic of Sciences, Guangzhou, China. Email: yangyikai@scsio.ac.cn
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