Multi-stage evolution of mesoscale warm eddies in the Kuroshio Extension: a case study based on data-assimilative modeling

Mesoscale warm eddy shedding from the Kuroshio Extension (KE) is highly variable, and its evolution during the life cycle is affected by KE perturbations. Based on the Regional Ocean Modeling System with Multiscale Data Assimilation (MSDA-ROMS), this study simulates the evolution of warm eddies in the KE region and analyzes their dominant dynamical processes. The results show that from March to July 2023, three warm eddies detached from the north flank of the KE underwent complex evolution processes, including repeated shedding from and reattachment to the KE jet, along with merging and separation among eddies. These repeated evolution events have weakened the typical bowl-shaped vertical profile of the initially formed warm eddies. Moreover, all separation and merging events were strain-dominated at interaction zones. Diagnostic analysis suggests that events triggered by KE perturbations are dominated by barotropic instability, whereas events triggered by the intrusion of the surrounding eddy are dominated by baroclinic instability in this case study. This study reveals an intricate case composed of several rapid warm eddy evolution events characterized by weekly to monthly timescales, providing a unique perspective for analyzing multiscale ocean dynamic processes in the KE region.