Internal tides over abrupt topography in the Southern California Bight: Observations of diurnal waves poleward of the critical latitude

Abstract

In the ocean, a mechanism for baroclinic internal tide generation is through the interaction of barotropic tidal currents with topography. Velocity profiles from a bottom-mounted acoustic Doppler current profiler are used to characterize the tidal generation of diurnal and semidiurnal internal modes over a ridge atop an abrupt 30° bathymetric slope in the Southern California Bight. This location is poleward of the critical latitude for diurnal frequency internal waves, yet the circulation is dominated by the diurnal internal tide. Overall, the structure of the diurnal internal tide resembles the first baroclinic mode. However, the mode is topographically distorted in the lower water column where it is amplified and polarized in the cross-ridge direction. The behavior of the diurnal response is contrasted with the nearly ideal appearance of the semidiurnal response. The diurnal baroclinic mode occurs as a persistent response to tidal forcing rather than because of the diurnal sea breeze as has also been suggested as an explanation for internal diurnal tides in other areas of the Southern California Bight. Copyright 2008 by the American Geophysical Union.