4:00 PM - 4:15 PM
[AOS19-03] Horizontal physical structure and mixing process in the inner part of Tokyo Bay using long-term monitoring data
Keywords:Tokyo Bay, Stratification, Mixing
In coastal regions such as Tokyo Bay, numerous physical structures are involved by the combined external forces, e.g., river water inflow, wind stress, and tides. Although there have been numerous studies on the physical structure in Tokyo Bay, few studies have focused on the mixing processes in the inner part of the bay. A previous study showed the mixing parameter from the observation data of a single mooring point in the northeastern part of Tokyo Bay (Itozu and Masunaga, 2021). However, mixing associated with horizontal physical structures has not been investigated in previous studies. In this study, we analyzed data from long terms observations at five monitoring point located in the inner part of the bay to understand physical structures associated with mixing processes. The observation data showed that a strong relationship between hypoxia water and high density water in the bottom layer was confirmed at all mooring points. The horizontal Richardson number (Rix) (Burchard, 2009), calculated from the wind, tide and horizontal density gradient, was significantly correlated with bottom DO. In addition, Rix was significantly corrected to the gradient Richardson number (Ri), which represents instability of the water column can be explained by the horizontal density gradient and wind stress. The horizontal salinity gradient in the inner part of Tokyo Bay tended to be larger than that in the middle of the bay. The horizontal salinity gradient was positively correlated with the river discharge of the four major rivers (Edo River, Arakawa River, Tama River, and Tsurumi River), with a time scale of about 10 days. Thus, the horizontal density gradient is caused by river discharges into the bay. These results indicates that vertical mixing in the inner part of Tokyo Bay can be explained by the wind stress and river discharges.