Barotropic and Baroclinic Tides over the Continental Slope and Shelf off Oregon

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  • 1 Department of Oceanography, University of Washington, Seattle 98195
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Abstract

During the Coastal Upwelling Experiment of 1973, several current meter moorings were deployed on the Oregon continental shelf and slope. Data from 16 current meters and temperature sensors which were deployed along a line perpendicular to the bathymetric contours were analyzed by the response method of tidal analysis (Cartwright et al., 1969). The diurnal tidal current was predominantly barotropic over the slope and shelf. The semi-diurnal current was strongly baroclinic. Semi-diurnal characteristics were computed from the model of Mooers (1970, 1975a) using STD data taken during the period of mooring deployment. The computed semi-diurnal characteristics, combined with the distribution of signal-to-noise ratios and the phase of the horizontal and vertical velocities, are consistent with generation of the internal tide as a wide beam (∼80 m) along the continental slope between 474 and 1050 m. The beam reflects from the sea surface and from the sea floor over the shelf as it passes through the mooring sites. The beam is present at least 50 km from the generation area. Barotropic and baroclinic components of the current were separated at each sensor. It was shown that the baroclinic components satisfy the momentum balance for internal waves. Baroclinic currents were as large or slightly larger than barotropic currents, which is consistent with available models. Baroclinic dissipation rates in mid-shelf and inner shelf regions (1.5 × 10−5 W m-3) are comparable to those found by Wang and Mooers (1977) for the same data set but using different methods of analysis. Baroclinic energy was dissipated more strongly on the outer shelf (2.5 × 10−5 W m−3).

Abstract

During the Coastal Upwelling Experiment of 1973, several current meter moorings were deployed on the Oregon continental shelf and slope. Data from 16 current meters and temperature sensors which were deployed along a line perpendicular to the bathymetric contours were analyzed by the response method of tidal analysis (Cartwright et al., 1969). The diurnal tidal current was predominantly barotropic over the slope and shelf. The semi-diurnal current was strongly baroclinic. Semi-diurnal characteristics were computed from the model of Mooers (1970, 1975a) using STD data taken during the period of mooring deployment. The computed semi-diurnal characteristics, combined with the distribution of signal-to-noise ratios and the phase of the horizontal and vertical velocities, are consistent with generation of the internal tide as a wide beam (∼80 m) along the continental slope between 474 and 1050 m. The beam reflects from the sea surface and from the sea floor over the shelf as it passes through the mooring sites. The beam is present at least 50 km from the generation area. Barotropic and baroclinic components of the current were separated at each sensor. It was shown that the baroclinic components satisfy the momentum balance for internal waves. Baroclinic currents were as large or slightly larger than barotropic currents, which is consistent with available models. Baroclinic dissipation rates in mid-shelf and inner shelf regions (1.5 × 10−5 W m-3) are comparable to those found by Wang and Mooers (1977) for the same data set but using different methods of analysis. Baroclinic energy was dissipated more strongly on the outer shelf (2.5 × 10−5 W m−3).

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