[A-OS14] Coastal physical processes associated with mixing, eddies, internal waves

[AOS14-05] Water mass classification off the east coast of Japan mainland using Regional Ocean Modeling System (ROMS)

*Masashi Ikeda¹, Eiji Masunaga¹, Yusuke Uchiyama², Yota Suzue⁴, Sachihiko Itoh³ (1.Ibaraki University , 2.Kobe University, 3.The University of Tokyo, 4.CTI Engineering)

Keywords:Water mass classification, Oyashio, Kuroshio

Marine environments off the Sanriku Coast are important for oceanic ecosystems and influence fishing grounds in the North Pacific Ocean. The T-S (Temperature - Salinity) combination has been frequently used for understanding water masses off the Sanriku Coast (e.g., Hanawa and Mitsudera., 1987). However, the water mass classification based on T-S diagram proposed by Hanawa and Mitsudera cannot explain seasonal variations of water masses in the surface layer. This study investigated the seasonal variation of water masses off the Sanriku coast using the Regional Ocean Modeling System (ROMS). The quality of the ROMS model was validated by comparing with the observed data obtained by the Iwate Prefectural Fisheries Laboratory. Model results well matches to the observed data. We have developed a method for the water mass classification for the three water masses of the Tsugaru Warm Current, Oyashio and Kuroshio using the normalized T-S combination. The normalized T-S diagram is computed from normalized temperature and salinity data with the standard deviation of unity. Three water masses (Tsugaru Warm Current, Oyashio, Kuroshio) were classified based on the distance between each T-S data and the three water masses on a normalized T-S diagram. Original T-S combinations of the Tsugaru Warm current, Oyashio, and Kuroshio were taken from averaged T-S values in Tsugaru Strait, Kuroshio Current Axis, and off Cape Erimo of Hokkaido, respectively. The three water masses were reasonably separated in the surface layer by this method and were not appropriately separated by a previously used conventional method. The water mass classification using this method is consistent with the velocity field of the surface layer. The area of the Oyashio water in the study area is majorly influenced by seasonal variations of the Tsugaru Warm Current.