LES study of near-seabed tide-induced turbulence in the East China Sea

Near-seabed turbulent properties observed in the East China Sea were investigated using a large eddy simulation (LES) model. Tidal forcing estimated from the observed tidal current is imposed to the LES model assuming a flat seabed. Turbulence stirred by tidal currents near the seabed is simulated and compared to observed turbulence. The observed tide is dominated by the M₂ constituent. The energy dissipation rate evolves with a quarter-day period near the seabed, whereas the dissipation rate evolves with a diurnal period in the upper part of the boundary layer. Salinity also oscillates diurnally. Thickness of the boundary layer related to K₁ is thicker than that of M₂. Orientation of the major axis of M₂ in the tidal ellipse does not change downward, but that of K₁ rotates counterclockwise. The vertical structure difference of two constituents is attributable to the observation site latitude, which is approximately the critical latitude of K₁. All of these features are simulated in the LES model. Particularly, results show that the interference of M₂ and K₁ induces diurnal variation of the turbulent dissipation rate in the upper part of the boundary layer through the turbulent energy production rate controlled by the vertical shear. A hypothetical simulation without horizontal advection demonstrate that this process can contribute more to the diurnal variation in the upper part of the boundary layer than stratification stability control owing to salinity advection through tidal straining.