Abstract
This paper proposes an algorithm named EddyGraph for tracking mesoscale eddy splitting and merging events. Twenty-seven years (January 1993–December 2019) of sea level anomaly (SLA) data are analyzed in the Northwest Pacific Ocean (105°E–165°W, 0°N–60°N). First, we propose a multilevel eddy identification method based on SLA to obtain an eddytree data set, representing a spatial topological tree structure of closed SLA contours with mononuclear eddies, multicore eddies and eddy seeds as the leaf nodes and eddygroups (reflecting the spatial topological relationship among eddies) as the intermediate nodes. The EddyGraph tracking algorithm is applied to the eddytree data set, which results in eddy-directed acyclic graphs (Eddy-DAGs). Only eddies contained within a common eddygroup are tracked as sources in merging events or sinks in splitting events. Furthermore, we extract typical splitting and merging events and composite the sea surface temperature anomalies (SSTAs) inside the eddygroups and eddies during these events. The results confirm that merging eddies in the same eddygroup degenerate into a single eddy and that a splitting eddy evolves into eddies within the same parent eddygroup. Moreover, we match a merging event of cyclonic eddies with in situ data of both drifters and loopers in Lagrangian trajectories. Finally, we present EddyGraph, a data set of mesoscale eddy tracking in the Northwest Pacific Ocean (105°E–165°W, 0°N–60°N).
Highlights
Mesoscale eddies play important roles in the exchange of energy and the mass transport of heat, nutrients, salt and other seawater chemical elements throughout the ocean [1,2,3,4,5,6,7,8,9,10,11,12]
No corresponding data set of eddy trajectories that considers splitting and merging behaviors has been published, and no data validation has been presented
(1) We propose an sea level anomaly (SLA)-based multilevel eddy identification method to establish the eddytree data set, a spatial topological tree structure of closed SLA contours with eddies as the leaf nodes and eddygroups as the intermediate nodes
Summary
Mesoscale eddies play important roles in the exchange of energy and the mass transport of heat, nutrients, salt and other seawater chemical elements throughout the ocean [1,2,3,4,5,6,7,8,9,10,11,12]. Cui et al [33] presented a method to define multicore structures in eddy–eddy interactions and took them as tracking objects for eddy splitting and merging events. It remains difficult to conduct normalized verification experiments, which are standard operations for validating the eddy-induced heat transport [1,8,9], to determine how multiple eddies merge into a new eddy and how a single eddy splits into different eddies. Another automated method, the Angular Momentum Eddy Detection and Tracking Algorithm (AMEDA), based on velocity fields was proposed [23].
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