UBC Theses and Dissertations

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UBC Theses and Dissertations

Oceanic turbulence Nasmyth, Patrick Walden

Abstract

In two experimental operations in deep water off the west coast of British Columbia, temperature and velocity microstructure have been recorded with a spatial resolution of 2 millimeters or better, from the thermocline down to a depth of 330 meters. Some measurements have been taken along horizontal paths at discrete depths, and, by superimposing a cycling vertical velocity on the constant forward motion, others have been taken along "saw—tooth" paths, revealing some new features of the fine structure of the ocean and the occurrence of turbulence below the thermocline. On one occasion sea-water conductivity was also measured, enabling the computation of density and examination of the occurrence and characteristics of the microstructure in relation to the density structure. Power spectra of velocity fluctuations have been computed and energy dissipation rates obtained. Estimates are made of mean energy dissipation as a function of depth and total dissipation throughout the ocean volume. The velocity spectra are compared with existing ideas of Kolmogoroff's universal spectral function for isotropic turbulence and discrepancies at high wavenumbers are attributed, at least in part, to the effect of buoyancy forces resulting from small scale density fluctuations. A new empirical version of the universal function is derived from what is considered to be the best ocean turbulence data available. Vertical transport of heat is calculated for a number of samples, from microscale measurements of temperature gradient and mean vertical gradient. A mean eddy coefficient of thermal diffusivity is estimated for the region.

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