Tidal currents seaward of the Northern California Continental Shelf

Abstract

Current measurements obtained from a sparse array of moorings deployed over the slope and the adjacent deep‐sea basin off northern California for 4 to 14 months have been analyzed for their tidal constituents. The M2 tidal currents were the strongest tidal constituent, containing 50% to 75% of the total current variance in the four major tidal bands. The semimajor axis of the M2 constituent ranged from 2 to 4 cm s−1 and tended to be aligned with the local topography. Internal tides, which were usually present in the M2 band, were often the dominant cross‐slope current component on the middle slope. At least a portion of the internal tidal current field had a steady phase that slowly changed over 1 to 2 months. The semimajor axes of the diurnal barotropic ellipses had amplitudes ranging from 0.7 to 1.2 cm s−1 and were oriented both parallel and perpendicular to the local topography. These tidal current measurements suggest that the barotropic diurnal currents propagate poleward as a combination of Kelvin and continental shelf waves and that the barotropic M2 tides propagate poleward primarily as a Kelvinlike wave. Battisti and Clarke's (1982) model, which uses coastal sea level data to predict M2 tidal currents, agrees reasonably well with the observations presented here, indicating that the model can be used to predict the M2 currents seaward of the middle slope off Northern California.