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A Microstructure Instrument for Profiling Oceanic Turbulence in Coastal Bottom Boundary Layers

Richard K. DeweyDepartment of Oceanography, University of British Columbia, Vancouver, B.C., Canada

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William R. CrawfordInstitute of Ocean Sciences, Sidney, B.C., Canada

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Ann E. GargettInstitute of Ocean Sciences, Sidney, B.C., Canada

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Neil S. OakeyBedford Institute of Oceanography, Dartmouth, N S., Canada

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Abstract

A free-falling instrument has been built to measure temperature, salinity and turbulent shear from near surface to within 15 cm of the ocean bottom. A probe guard mounted at the lower end of the instrument protects sensitive shear and temperature sensors from bottom sediments. The noise level in the shear signal corresponds to a dissipation rate of 3.0 × 10−7 W m−3, with vibrations of the probe guard providing the largest component of the noise. The signals are transmitted through a neutrally buoyant line to the ship where they are displayed in real time and recorded for later analysis. The profiling technique is capable of 20 profiles per hour through 50 m of water. Simultaneous profiles of turbulent microstructure and density can now be consistently obtained through the entire water column.

Abstract

A free-falling instrument has been built to measure temperature, salinity and turbulent shear from near surface to within 15 cm of the ocean bottom. A probe guard mounted at the lower end of the instrument protects sensitive shear and temperature sensors from bottom sediments. The noise level in the shear signal corresponds to a dissipation rate of 3.0 × 10−7 W m−3, with vibrations of the probe guard providing the largest component of the noise. The signals are transmitted through a neutrally buoyant line to the ship where they are displayed in real time and recorded for later analysis. The profiling technique is capable of 20 profiles per hour through 50 m of water. Simultaneous profiles of turbulent microstructure and density can now be consistently obtained through the entire water column.

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