Baroclinic semidiurnal tidal currents over the continental shelf off northern California

Abstract

Time‐varying depth‐dependent currents of semidiurnal frequency are identified in data collected over the northern California continental shelf during the 1982 up welling season as part of the Coastal Ocean Dynamics Experiment. An increase in semidiurnal band kinetic energy is seen during wind relaxation periods when stratification over the shelf and upper slope increases. Comparison with internal wave theory shows the vertical and horizontal structure of the semidiurnal band horizontal current and temperature fluctuations to be consistent with a first baroclinic mode internal wave with a horizontal wavelength of 20–30 km. Over the continental shelf the semidiurnal band temperature fluctuations show a phase shift which may be evidence of the influence of the subcritical bottom slope and/or the effects of bottom friction. The bottom slope is supercritical over the upper continental slope, suggesting that generation of the semidiurnal internal waves observed over the shelf may take place near the shelf break. Application of Baines' (1982) theory for the generation of internal tides underpredicts the observed baroclinic tidal currents.