[A-OS17] Ocean circulation and material cycle in coastal seas

[AOS17-04] Model results corresponding to of the observation around Oitsukami Island in the Bungo Channel for prediction of sudden coastal intrusion of Kuroshio water (Kyucho)

*Toru Miyama¹, Eisuke Tsutsumi², Naoki Yoshie³, Xinyu Guo³, Takahiro Endoh⁴, Yasumasa Miyazawa¹ (1.Japan Agency for Marine-Earth Science and Technology, Application Laboratory, 2. Faculty of Fisheries, Kagoshima University, 3.Center for Marine Environmental Studies, Ehime University, 4.Research Institute for Applied Mechanics, Kyushu University)

Keywords:turbulent mixing, tidal currents, sudden coastal intrusion of Kuroshio water (Kyucho), vertical eddy diffusion, ocean prediction, sparse principal component analysis

In the Bungo Channel, the occurrence of Kyucho, a sudden coastal intrusion of warm water from the offshore Kuroshio region, affects the ecosystem and fisheries along the coast of the Bungo Channel. It is necessary to accurate predict ocean states for preventing damage to fisheries by Kyucho. Application Laboratory of Japan Agency for Marine-Earth Science and Technology has developed an ocean prediction model with a horizontal resolution of 1/500° in the Bungo Channel (https://www.jamstec.go.jp/jcope/vwp/ sukumo/). Although the turbulent mixing process is important for the intrusion process of the Kyucho into the Bungo Channel, it is unclear how well the model reproduces the turbulent mixing process in the Bungo Channel. Therefore, we have conducted the observation with the support of Grant-in-Aid for Scientific Research project “Prediction and Understanding of Sudden Kuroshio Coastal Intrusion Processes by Integrating New Generation Satellites and Responsive Field Observations” (JP21H01444), and Leading Academia in Marine and Environment Pullution Research (LaMer) of the Center for Marine Environmental Studies (CMES), Ehime University. The observation was conducted by the research vessel "ISANA" of the CMES, and data on turbulence were obtained with a h a free-falling turbulence profiler, and data on current velocity with shipboard Acoustic Doppler Current Profilers (Tsutsumi et al., in another presentation). The results of sparse principal component analysis of the model suggest that the area around the Oitsukami Island has a different time variability from the southern part of the Bungo Channel and is influenced by the spring-neap tides cycle, where the sea surface temperature tends to decrease during spring tides. This was one of the rationales for conducting observations around the Oitsukami Island. Unfortunately, at the time of the survey, the Kuroshio was away from the Shikoku, and no Kyucho occurred. On the other hand, analysis suggests that its departure from the Shikoku Island reflects a unique path characteristic of the Kuroshio Large Meander that began in August 2017, and that this was a valuable observation opportunity under such a circumstance.The model captured the characteristics observed in the observation, such as the cold water around the Oitsukami Island compared to the surrounding area, hotter and fresher surface water and colder and saltier bottom water during the neap tide than the spring tide. Therefore, it is expected that the intercomparison between observation and model will help to understand what kind of phenomena were occurring.