Three-dimensional mesoscale eddy identification and tracking algorithm based on pressure anomalies

The Kuroshio Extension (KE) is one of the most eddy-energetic regions in the global ocean. However, most mesoscale eddy studies in the region are focused on surface eddies and the structure and characteristics of three-dimensional (3-D) eddies require additional research. In this study, we proposed a 3-D eddy identification and tracking algorithm based on pressure anomalies, similar to sea level anomalies (SLAs) for surface eddy identification. We applied this scheme to a 5-year (2008–2012) high-resolution numerical product to develop a 3-D eddy dataset in the KE. The reliability of the numerical product was verified by the 5-year temperature/salinity hydrological characteristics and surface eddy distribution. According to the 3-D eddy tracking dataset, the number of eddies decreased dramatically as the eddy existence-time increased and more anticyclonic eddies (AEs) had an existence-time longer than 1 week than cyclonic eddies (CEs). We presented daily variations in the 3-D structure of two 3-D eddy-tracking trajectories that exhibit a certain jump in depth and a shift toward the west and equator. In addition to the bowl, lens, and cone eddies that have been discovered by previous researchers, we found that there is a cylindrical eddy, and its eddy radii are almost consistent across all layers. CEs cause significant negative temperature anomalies, “negative-positive” salinity anomalies, and sinking current fields in the KE region, while AEs cause positive temperature anomalies, “positive-negative” salinity anomalies, and upward current fields. The four types of eddies have different effects on the temperature/salinity anomalies and current field distribution which are related to their structure.