Development of a Semi-Spectral Coastal Ocean Model and Its Application to the Neko Seto Sea in the Seto Inland Sea

Abstract

For studying coastal ocean processes, a new ocean model has been developed based on the semi-spectral method using three-dimensional primitive equations. The basic idea is that the vertical mode is used as a basis. As a first step in the development of the model, the Fourier cosine series is used as a basis by assuming that the reference density is homogeneous. To test the performance of the model, it has been applied to the regional model of the Neko Seto Sea in the Seto Inland Sea. The model result has been compared intensively with the observational result of acoustic Doppler current profiler (ADCP) on the eastern side of the Meneko Seto Strait. The model reproduced the realistic horizontal and vertical structure of the tidal current and vortices. The tidal current in Nigata Bay has been compared with a previous observational study. The generation process of the clockwise vortex at eastward flow is found to be different from the previous observational description. By using the vorticity analysis, it was found that the vortex stretching associated with the sloping bottom topography is essential to the generation of the counterclockwise vortex during eastward flow and the clockwise vortex during westward flow in Nigata Bay. On the other hand, the advection of vorticity from the edge-like coastal geometry is essential for the generation of the vortices on the eastern side of the Strait. However, the positive vorticity supply from tilting enhances the growth of the counterclockwise vortex, and is indispensable for reproducing its realistic position.