Some properties of tidal currents estimated from analytical and LES simulation studies

Abstract

Some features of tidal current ellipses near the ocean floor are estimated from the bottom-limit solutions of the tidal equations with constant eddy viscosity. It is verified that a clockwise rotating ellipse becomes broad descending through the bottom boundary, whereas a counterclockwise ellipse becomes narrow except near the critical latitude. The major axis of an ellipse near the floor is directed 45° leftward (rightward) against that of the overlying tidal flow ellipse poleward from the critical latitude in the northern (southern) hemisphere. Equatorward from the critical latitude, the major axis near the floor lines up with that of the overlying tidal current ellipse in both hemispheres. The retrograde rotating hodograph against the overlying clockwise tidal hodograph appears near the floor around the critical latitude. These features are confirmed from the numerical studies using the large eddy simulation model. The deflection of the major axis poleward from the critical latitude is a little smaller, about 19°. Furthermore, the effects of nontraditional Coriolis force resulting from the horizontal component of the earth-rotating vector on the development of turbulence were investigated. When the diurnal tidal current is directed westward, the effective vertical eddy viscosity becomes maximum with developing turbulence. While in the case of a semidiurnal tide, a northward tidal current is preferred for turbulence development.