Eddy evolution and water exchange mechanisms based on curvature vorticity diagnostics

Mesoscale eddies play a central role in ocean dynamics and material transport, with their rotational structures exerting significant regulatory effects on water exchange and transport processes. Based on high-resolution numerical simulations combined with curvature vorticity diagnostics, this study analyzes the dynamic evolution of cyclonic and anticyclonic eddies and their influence on water exchange. The results show that eddies form stable, closed circulation structures at the surface, effectively “trapping” water masses and significantly prolonging their exposure time. Meanwhile, the distribution of exposure time exhibits strong vertical dependence, with the spatial distribution evolving from a near-circular pattern at the surface to a more concentrated and asymmetric structure in the middle and bottom layers. At the eddy periphery, central Ekman suction and enhanced mixing jointly maintain both the enclosed nature of the eddy and the exchange activity along its boundary. Curvature vorticity diagnostics reveal that while the rotational structure strongly influences the distribution of exposure time, the dynamic evolution of cyclonic and anticyclonic eddies differs markedly. The early stage of anticyclonic eddy formation is dominated by the banking term, transitioning to dominance by the stretching term during the stable phase. In contrast, cyclonic eddies enter the unstable stage earlier, with their development mainly controlled by transport term and vortex stretching.