[A-OS12] Ocean Science Revealed by Global Observation System

[AOS12-07] The propagation features of sub-mesoscale frontal eddies along the Kuroshio revealed by SWOT observations

*Xiaoyu Zhao^1,2,3, Guihua Wang^1,2,3 (1.Department of Atmospheric and Oceanic Sciences Institute of Atmospheric Sciences, Fudan University, Shanghai, China, 2.Shanghai Frontiers Science Center of Atmosphere-Ocean Interaction, Fudan University, Shanghai, China., 3.CMA FDU Joint Laboratory of Marine Meteorology, Fudan University, Shanghai, China. )

Keywords:Frontal eddies, SWOT, Kuroshio, Propagation speed, Numerical simulation

Based on multiple satellites, especially the Surface Water and Ocean Topography (SWOT) mission, the propagation characteristics of frontal eddies (FEs) southeast of Kyushu along the Kuroshio were investigated. These frontal eddies propagate downstream at speeds ranging from 0.1 to 0.6 m/s—exceeding previous estimates. The dynamic evolution of a FE case captured by SWOT shows an increase in equivalent radius from 10 km to 30 km and in amplitude from 3 cm to 13 cm. Numerical simulation results show that FEs slow down during growth, displaying a tilting propagation pattern reaching depths of 250 m. An empirical model was developed to estimate eddy propagation speed, considering local Kuroshio velocity, eddy size, and wind stress. Regression analysis indicated that local Kuroshio velocity is the dominant factor, with eddy size and wind stress also contributing. This study highlights that the FE propagation speed is approximately 60% of the local Kuroshio flow velocity, with their downstream trajectory modulated by the Kuroshio's path. The FEs slow down by about 20% as their sizes increase after normalization. This means smaller eddies move faster under favorable conditions of strong currents and weak opposing winds. This study revealed frontal eddies' behaviors as submesoscale processes mainly regulated by the western boundary current system.