Quantification and characterization of mesoscale eddies with different automatic identification algorithms

ABSTRACT Viikmäe, B., Torsvik, T., 2013. Quantification and characterization of mesoscale eddies with different automatic identification algorithms Automatic methods for detection of mesoscale eddies are usually based on either physical (e.g. Okubo-Weiss parameter) or geometrical (e,g, streamline winding-angle) flow characteristics. In this paper, a hybrid method combining the strengths of the two different approaches is applied to the Eulerian velocity fields for two case studies: (i) the Gulf of Finland (the Baltic Sea) and (ii) the Raunefjord and Vatlestraumen area south-west of Bergen, Norway. Velocity fields are investigated with a hybrid winding-angle method (HWA), where the Okubo-Weiss parameter is first used to detect potential eddies, and the winding-angle method is used locally within these regions to test the Okubo-Weiss result. In the Gulf of Finland, the HWA method results in a substantially reduced number of detected eddies compared with the Okubo-Weiss result, indicating that the Okubo-Weiss parameter severely overestimates the number of eddies. In Vatlestraumen, there was a better correspondence between results obtained by the HWA and the Okubo-Weiss methods. The HWA method requires careful analysis since more than one streamline may identify the same eddy structure.

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