Profiler Measurements of Vertical Velocity Fluctuations in the Ocean

J. N. Moum College of Oceanography, Oregon State University, Corvallis, Oregon

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Abstract

A method is described for measuring the vertical component of velocity fluctuations due to three-dimensional turbulence in the ocean from a freely falling microstructure profiler. The dynamic pressure measurement relies on a commercially available and very sensitive piezoresistive differential pressure transducer. At nominal profiler fall speeds of 0.9 m s−1, the noise limit in vertical velocity fluctuations is ∼3 mm s−1. Scaled turbulence spectra from shear probes and from the new sensor demonstrate the validity of the measurement. Although hydrodynamic noise (eddy-shedding) at frequencies near the peak in the dissipation spectrum precludes full resolution of the high wavenumber portion of the spectrum, the high end of the inertial subrange of the turbulence is resolved. At low wavenumbers, the measurement is limited by the finite size of the profiler. It is anticipated that the method will be useful in examining turbulent fluxes using an eddy-correlation technique.

Abstract

A method is described for measuring the vertical component of velocity fluctuations due to three-dimensional turbulence in the ocean from a freely falling microstructure profiler. The dynamic pressure measurement relies on a commercially available and very sensitive piezoresistive differential pressure transducer. At nominal profiler fall speeds of 0.9 m s−1, the noise limit in vertical velocity fluctuations is ∼3 mm s−1. Scaled turbulence spectra from shear probes and from the new sensor demonstrate the validity of the measurement. Although hydrodynamic noise (eddy-shedding) at frequencies near the peak in the dissipation spectrum precludes full resolution of the high wavenumber portion of the spectrum, the high end of the inertial subrange of the turbulence is resolved. At low wavenumbers, the measurement is limited by the finite size of the profiler. It is anticipated that the method will be useful in examining turbulent fluxes using an eddy-correlation technique.

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