Satellite observed shape-based overall rotation—A new aspect in eddy kinematics

With the development of satellite altimetry technology, the resolution of sea-level anomaly (SLA) datasets is constantly improving. Current spatial resolution levels can reach a grid size of (1/4)° × (1/4)°, with daily measurements that span from 1993 to 2018, allowing for the precise identification and tracking of individual eddies. In the current study, in addition to the internal circulation and migration of eddies, a new aspect in eddy kinematics is revealed and investigated for the first time: shape-based overall eddy rotation (SOER), based on the intrinsic elliptical shape of eddies identified from a high-resolution SLA dataset. We found that eddies can maintain an elliptical shape and a slow and stable SOER during their migration process. The SOER speed was observed to be negatively correlated to eddy lifetime, and exhibited a dependence on latitude, decreasing from low- and high- to mid-latitudes. The SOER direction tended to be consistent with the direction of internal circulation, particularly for long-lived eddies. In addition, we identified a negative relationship between internal circulation speed and SOER speed while the migration speed was positively related to SOER speed. These findings further expand and improve eddy kinematics, which is of great significance for the future study of eddy dynamics.