We analyze a concurrent simulation result of the ocean circulation and tidal currents using a data‐assimilative ocean general circulation model covering the Western North Pacific with horizontal resolution of 1/36° to investigate possible interactions between them. Four sites of active M2 internal tide variability in open ocean (hot spots), such as Tokara Strait, Izu Ridge, Luzon Strait, and Ogasawara Ridge, are detected from both the satellite observation and the simulation. Energy cycle analysis of the simulated M2 baroclinic tide indicates two types of the hot spots: dissipation (Tokara Strait and Izu Ridge) and radiation (Luzon Strait and Ogasawara Ridge) dominant sites. Energy conversion from barotropic to baroclinic M2 tides at the hot spots is modulated considerably by the lower‐frequency changes in the density field. Modulation at the two spots (Tokara Strait and Izu Ridge) is affected by the Kuroshio path variation together with the seasonal variation of the shallow thermocline. At the other two sites, influence from changes in the relatively deep stratification through the Kuroshio intrusion into South China Sea (Luzon Strat) and mesoscale eddy activity (Ogasawara Ridge) is dominant in the modulation.
[1] The Ryukyu Current System (RCS) is a northeastward current southeast of the Ryukyu Islands. The variation of current structure in the RCS region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data. Three realizations of the RCS are examined from cruises in May, September, and October 2002. It was found that the current structure in the RCS region is divided into upper and lower layers by an isopycnal surface of 26 s q . The currents in both layers proceed northeastward along the eastern slope, east of the Ryukyu Islands. The current in the upper layer merges with the inflow from the interior region, resulting in larger northeastward volume transport southeast of Amami-Oshima Island than southeast of Okinawa Island. The volume transport from the east reaches more than 40% of that southeast of Amami-Oshima Island. On the other hand, the current in the lower layer is not affected by inflow from the east. It is also found that the upper RCS gains heat mainly through the advection of warm water from the east, resulting in an increase in the downstream temperature by about 0.5°C on average.
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