Observations and Analysis of the Internal Tide in the Monterey Bay Region
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The Monterey Bay region, with bathymetric features including Monterey Submarine Canyon and Sur Platform, has been a site for examination of generation, propagation and dissipation of the internal tide. Observations of propagation of the internal tide on the California continental margin and in Monterey Submarine Canyon are presented. Additionally, the development and sea-trials of the EM-POGO, a free-falling absolute velocity profiler which can be used to study the internal tide is detailed. <bold>EM-POGO:</bold> The EM-POGO is a low-cost and accurate velocity profiler. Electromagnetic current instrumentation has been added to Bathy Systems, Inc. POGO transport sondes to produce the EM-POGO. Velocity determined from measurements of motionally-induced electric fields generated by ocean currents moving through the vertical component of the Earth's magnetic field are added to the transport provided by the POGO. A refurbished EM-POGO collected 15 profiles; relative and absolute velocity uncertainty was &sim 1 cm s<super>-1</super> and 0.5 – 5 cm s<super>-1</super>, respectively, with 25-m vertical resolution. <bold>Internal tide:</bold> North of Sur Platform but south of Monterey Submarine Canyon, a short-duration survey and a multi-week timeseries measured northward energy flux in the mean, supporting model results indicating that topographic features off Point Sur generate strong internal tides observed in the canyon. Though dominated by low modes with O(100 km) horizontal wavelengths, semidiurnal energy fluxes, kinetic and potential energies show lateral variability on O(5 km) scales. Spatial variability results, in part, from interference patterns and the sharp delineation of beams with limited azimuthal extent. A simple two-source model of a first-mode interference pattern reproduces the most striking aspects of the observations. In Monterey Submarine Canyon energy fluxes are steered by canyon bathymetry and are consistent with a numerical model. Vertical profiles reveal predominantly along-canyon flux intensified in the bottom 500 m. A rough one-dimensional along-canyon energy budget based on energy-flux divergence, dissipation rates and barotropic-to-baroclinic energy conversion rates is constructed. Cross-canyon- integrated along-canyon flux decreases from 13 ± 3.4 MW at the deepest section (1500 m) to 5.6 ± 0.3 MW at the shallowest (900 m). The largest drops ( ∼ 7 MW and ∼ 4 MW) are around meanders. The one-dimensional flux budget is, on average, balanced.
- Oceanography