Shigeru Tabeta

Comparison of simulation results and field data on currents and density in Tokyo Bay

A multilevel model was applied to the calculation of permanent current and density variation in Tokyo Bay, and the change of the state of stratification and the accompanying current field was simulated. In the numerical simulation, the observed field data such as wind conditions and atmospheric temperature were used as input to the calculation, and the results were compared with the observed values of currents, salinity, and sea temperature. Comparison of simulation results and observed data revealed that the numerical simulation could describe well the current and density field governed by wind under stratified conditions. In particular, the long-term variations of the vertical structure of salinity and temperature from summer to autumn could be predicted qualitatively, as could the long-term variations of the vertical structure of salinity and temperature from summer to autumn. Additionally, the effects of boundary conditions on the results of numerical simulations were examined. As a result, it was clarified that the simulation results of salinity stratification were strongly affected by the boundary conditions such as river discharge and the vertical structure of salinity at the open boundary adjacent to the outer ocean.

A study on real time simulation of oceanophysical environment in Tokyo Bay

A group of university researchers and Technological Research Association of Mega-Float made continuous measurement of temperature and salinity of the sea water around Mega-Float model, moored off Oppama, from August 1996 till December 1998. The purpose of the measurement was to examine the impacts of Mega-Float on surrounding marine environment and it was found that the effects were very small. In the meantime, these observation data is very useful for the verification of the results of numerical simulations which is thought to be one of the useful tools for environmental impact assessment. So we calculated the current flow, water temperature and salinity in the summer of 1996 in Tokyo Bay. In numerical simulation, to compare the results of numerical simulation with observation data directly, we use the observed field data such as the amount of solar radiation, wind velocity and direction, etc. as boundary conditions. Additionally, the effects of boundary conditions on the results of numerical simulations were also examined. It was clarified that the variations of water temperature and salinity were predicted well quantitatively and the simulation results are affected by the boundary conditions such as extinction coefficient of sunlight and wind velocity.