Analysis and Interpretation of Tidal Currents in the Coastal Boundary Layer.

摘要

The Coastal Boundary Layer Transect (COBOLT) experiment was conducted within 12km of the south shore of Long Island,New York to elucidate the characteristics of the coastal boundary layer in the Middle Atlantic Bight. Analysis of data from this experiment show that 35% of the kinetic energy of currents averaged over the 30 m depth are due to the semidiurnal and diurnal tides. Tidal ellipses show considerable vertical structure which can be explained adequately by a local constant eddy viscosity model with a slippery bottom boundary condition. The major axis of the tidal ellipse formed from the depth averaged semidiurnal currents is not parallel to the local shoreline but is oriented at an angle of about -15degrees. This orientation 'tilt'is a consequence of the onshore flux of energy,computed to by about 800watts/m,and can be explained with a simple model employing long,rotational gravity waves (Sverdrup waves) and an absorbing coastline. Internal oscillations of tidal frequency also occur in the COBALT data. These are primarily at diurnal frequencies and may be Doppler-shifted by the mean currents of the coastal region.