A Global Eddy Splitting and Merging Trajectory Dataset Based on Satellite Altimetry Utilizing Eddygroup, Eddytree and Eddygraph

Abstract. The splitting and merging of mesoscale eddies constitute significant dynamical processes and remain a central subject of investigation in oceanographic research. An eddy is defined as a closed contour derived from satellite altimetry data that encloses a seed point (a local extremum), while a closed contour containing multiple eddies and seed points is identified as an eddygroup. The eddytree is a rooted hierarchical tree structure in which eddygroups and eddies are organized by spatial containment. An efficient global algorithm is developed for the identification of mesoscale eddies and eddygroups, and an eddygroup area-based ranking algorithm is further proposed for constructing eddytrees. Compared with existing approaches, the overall computational efficiency is enhanced by a factor of eleven. For eddy tracking, a particle-drift method is applied to track the splitting and merging between eddygroups and eddies at the terminal nodes of the eddytree, which are ultimately connected into eddy directed acyclic graphs (referred to as eddygraphs). Based on these methods, a 31-year (January 1993–December 2023) global dataset of mesoscale eddies and eddygroups, as well as a trajectory dataset of eddy splitting and merging, is constructed. These datasets provide valuable references for advancing research on ocean dynamics and climate variability. Furthermore, statistical analyses of the 31-year identification results reveal the existence of relatively stable and persistent cyclonic and anticyclonic eddytree structures within the ocean. These structures correspond closely with large-scale ocean circulation patterns: anticyclones dominate in regions of strong western boundary currents; boundaries between cyclonic and anticyclonic eddytrees emerge at confluence zones of warm and cold currents; and island wake regions exhibit von Kármán–type vortex-street structures. Finally, we normalize and characterize the morphological evolution of eddygroups and eddies during splitting and merging processes. The analysis shows that before merging, pairs of eddies typically take on egg-shaped morphologies, which remain after merging, with the smaller eddy corresponding to the sharp pole of the egg-shaped structure. Similarly, before splitting, eddies also exhibit egg-shaped forms, and after splitting, the smaller eddy corresponds to the sharp pole of the pre-split structure. During this process, the research found that the common parent eddygroup plays an important role in the morphology of the splitting and merging events, where the boundary of the resultant eddy after merging is a degeneration of the boundary of the two pre-merging eddies' common parent eddygroup, while before splitting, the boundary of the single eddy evolves into the common parent eddygroup of the two post-splitting eddies. This also reveals the reciprocal nature of the dynamic processes of eddy splitting and merging. The dataset is publicly available via: https://data.casearth.cn/dataset/68a3e04d913dfd1b2d6cbd76 (Tian et al., 2025).