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

[AOS17-01] Kinetic energy dynamics associated with baroclinic and barotropic motions in Tokyo Bay

*Koyomi Watanabe¹, Haruki Itozu¹, Eiji Masunaga¹ (1.Ibaraki University)

Keywords:Tokyo Bay, kinetic energy, baroclinic and barotropic motions

In semi-closed inner bays such as Tokyo Bay, in addition to tidal forcing, non-tidal components caused by wind and other external forces play an important role in water circulations. Winds largely contribute to vertical mixing and upwelling of hypoxic water masses. Although previous studies have shown stratification and hypoxia water in Tokyo Bay and their influence in oceanic environments, previous works did not report details of e.g., periodic motions (tides and internal tides) and wind-induced flows in the inner part of Tokyo Bay. In this study, we analyzed data from long-term observations at monitoring posts located in the inner part of the bay to investigate the effects of barotropic/baroclinic, tidal/non-tidal motions and their frequency characteristics. Observed flows are divided into tidal and non-tidal currents, and these components are decomposed into barotropic and baroclinic currents. The observation data showed that the non-tidal baroclinic component is larger in summer in the inner bay. The relationship between the stratification and the kinetic energy of the non-tidal baroclinic component shows a clear positive correlation. The horizontal density gradient also shows a clear positive correlation related to the kinetic energy of the non-tidal baroclinic component. Strong non-tidal baroclinic component in summer at shallower depths is caused by an enhanced estuarine circulation due to summer stratification. The intensified summer stratification is not only explained by river discharge, but also the warm surface layer. In addition, the four components are decomposed into long-period and short-period components with a cut-off period of 36 hours. We will also present about frequency characteristics of motions in the bay. These results indicate that motions and circulations in the inner part of Tokyo Bay can be explained by the wind stress and the strength of the stratification.