A Numerical Study of the Seasonal Differences of Circulation Processes in a Nearly Closed Coastal Basin

A vertical grid, two-dimensional finite difference method was employed to simulate the seasonal differences of the circulation processes in a nearly closed coastal bay with two deep basins. The observed heat flux at the sea surface, the water inflow into the north basin, and the temperature and salinity distributions at the open boundary were utilized for numerical simulation. The mixing in winter and stratification in summer were seen in the resulting density current, and the temperature and salinity distributions. The densities in the lower layers of the basins slowly decreased from winter to autumn, and rapidly increased from autumn to winter. The absolute value of the density current in winter was found to be almost 10 times larger than that from spring to autumn. The water mass exchange of the south (north) basin was calculated to be 5•4 times (5•8 times) year−1, and its greater part was realized in winter. These results show that the heating/cooling of the estuarine surface affects the weakly mixed/well mixed characteristics of the estuary. This difference leads to enhanced water exchange in winter compared to that in summer, particularly in the temperate zone such as that modelled in this paper.