[A-OS18] Kuroshio Large Meander

[AOS18-P01] Characteristics and evolution of the cyclonic eddy in the Kuroshio coastal area in association with the Kuroshio large meander

★Invited Papers

*Daiki Ito¹, Takashi Setou¹, Daisuke Ambe¹, Yugo Shimizu^1,2 (1.Fisheries Resources Institute, Japan Fisheries Research and Education Agency, 2.(Present affiliation) Fisheries Agency)

Keywords:Potential vorticity, Small meander, Eddy-eddy interaction

The Kuroshio coastal area, which is located between the south coast of Japanese islands and the Kuroshio, is nutrient-rich and becomes a major spawning grounds of various fishes. This area is occupied by the cyclonic eddy in association with the Kuroshio large meander. Therefore, during the Kuroshio large meander period, dynamical structures and evolutions of the cyclonic eddy greatly influence the marine resources and fisheries through the variation of the marine environment such as temperature, salinity (S) and dissolved materials. In addition, previous studies have demonstrated that the dynamical evolution of the cyclonic eddy is a key factor to predict the generation and decay of the Kuroshio large meander. While the monitoring and analysis of the cyclonic eddy are necessary in understanding of the dynamical processes and the variability of the marine resources, studies based on the observation are limited. To examine the characteristics and evolution of the cyclonic eddy in the Kuroshio coastal area in association with the Kuroshio large meander, we conducted hydrographic surveys in and around the cyclonic eddy and its upstream region in September 2020, along with analyzing fixed line observation data along 138°E during the Kuroshio large meander period. The low-Sand high-potential vorticity (Q) water in the surface layer was found in the Kuroshio coastal area from the small meander southeast of Kyushu to the cyclonic eddy. The high-Q water was in the similar density range, suggesting the supply of high-Q water into the cyclonic eddy from the upstream region. On the other hand, a cold eddy pinched off from the cyclonic eddy had a core of high-Q in the different density range from the cyclonic eddy. Eddy-eddy interaction associated with the Kuroshio large meander was discussed using the observation data, with particular attention to the magnitude of Q, the depth of cores, and the size of eddies. Moreover, the analysis of the fixed line observation data along 138°E showed the temporal variation of Q in the cyclonic eddy from 2017 to 2021.