Numerical Simulation of Tidal Currents by means of Multi-level Model

A multi-level simulation program was developed to compute the ocean current. As an example of its application, tidal currents of 12 hours period in Tokyo Bay were calculated and compared with observations. As a result, it was found that computed results of tidal ellipses, amplitude and phase lag of tidal elevation agree fairly well with observed ones. The most striking characteristic feature of multi-level model is to be able to clarify the vertical structure of tidal currents, i. e., the distribution of vertical velocity and the structure of vertical shear current. In the numerical simulation of ocean currents, a part of various parameters included in governing equations are usually determined empirically. In order to examine the influence of such parameters on computed results, a series of comparative simulations were carried out varying the numerical values of such parameters in a systematic manner. Furthermore, the effects of river inflow and seasonal wind direction on the tidal residual flow were clarified. In particular, the difference in tidal currents predicted by the simulation model with different number of levels was discussed in detail.