Three‐dimensional modeling of tidal currents and mixing quantities over the Newfoundland Shelf

Abstract

Major semidiurnal (M2, S2, and N2) and diurnal (K1 and O1) barotropic tides over the Newfoundland Shelf are computed using a three‐dimensional nonlinear primitive equation model, with the vertical eddy viscosity calculated from a level 2.5 turbulence closure scheme. Computed elevation cotidal charts for the five constituents are generally consistent with previous knowledge for this region. Comparisons based on a statistical analysis of the differences between the computed elevations and currents and in situ observations indicate good agreement. While M2 tidal currents (up to 20–30 cm/s) are dominant, there are locally intensified diurnal currents (up to 5–10 cm/s) in some outer shelf locations. The diurnal current intensification is attributed to first‐mode continental shelf waves. An examination is carried out for the vertical structure of the computed M2 current and for the temporal and spatial variability of model turbulent kinetic energy, mixing length scale, vertical eddy viscosity, and bottom friction velocity. The examination indicates that large vertical eddy viscosity magnitudes and bottom friction velocities are associated with strong currents in shallow regions, where strong vertical shears produce large turbulent kinetic energy. Solutions with both specified and evolving vertical stratification indicate that the stratification has a significant influence on the vertical profile of tidal mixing parameters and currents in shallow areas. Tidally induced turbulence is substantially reduced in the bottom boundary layer and completely suppressed above it. Tidal currents decrease in the log layer, increase significantly in the rest of the bottom boundary layer, and decrease in the upper and middle water column.