Long-Term Variation in Mesoscale Eddy Activity Around the Kuroshio in the East China Sea During 1993–2023

Mesoscale eddies are highly active around the Kuroshio in the East China Sea (ECS), serving as a crucial component of the ECS’s complex dynamic environment. However, the long-term variation in mesoscale eddies in this region has not been systematically investigated. Based on daily satellite altimeter data spanning from January 1993 to December 2023, this study comprehensively investigates the trend characteristics of mesoscale eddies in the ECS during this period, using eddy metrics such as Eddy Kinetic Energy (EKE) and eddy polarity probability. EKE in the ECS is primarily high around the Kuroshio, exhibiting a significant increasing trend. This upward trend is more pronounced in summer, autumn, and winter, all of which pass the significance test. From the statistics of coherent mesoscale eddies, cyclonic and anticyclonic eddies show opposite trend characteristics: cyclonic eddies display trends of decreasing number and weakening intensity, while anticyclonic eddies exhibit trends of increasing number and strengthening intensity. Energy transfer from the background flow makes a certain contribution to the aforementioned trends, but is relatively complex. The opposing trend characteristics exhibited by eddies of different polarities are related to the work done by the upper-ocean wind field. The nonuniform responses of wind-related changes in cyclonic and anticyclonic eddies could affect the regional patterns of ocean circulation and biogeochemical responses to future climate change.