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Cup anemometer wind observations over the sea

University of British Columbia

During the past two summers at the Institute of Oceanography of the University of British Columbia a research group has been involved in an experimental programme studying the interaction between the air and the sea close to the ocean surface. To date instruments have been developed and used to measure the vertical flux of momentum and the waves on the water surface. The observational site is situated on the tidal flat, Spanish Banks, in Burrard Inlet. Though the fetch is limited measurements are considered to be representative of the air flow close to the sea surface. The most important influence driving the ocean circulation is thought to be the momentum transferred through the atmospheric boundary layer. Although quantities such as heat and water vapour are also transferred, this thesis concerns only the transport of momentum. From profiles of wind speed measured over the sea at six heights up to five meters the downward transport of momentum is deduced. Whenever possible this momentum transport is compared to other estimations of this quantity, obtained by means of the hot wire anemometer. The various conditions of atmospheric stability are recorded and used in association with wind profile studies. Another important aspect of the wind profile study of this thesis is to determine the optimum averaging time for wind speeds in order that they may give meaningful estimates of the vertical transport of momentum. Furthermore, wind profiles are compared critically for fluctuating winds of approximately ten minute duration with the hope of discovering the influence of waves on the air flow close to the surface. The surface drag coefficients are inferred from the wind profiles and results are compared to those of other workers. The influence of the other measured variables on drag coefficients, such as wind speed, stability, and fetch, is studied. Several spectra of the low frequency downwind velocity fluctuations are computed and these results are compared with the spectra obtained by other workers and in addition with a hot wire anemometer spectrum. For one run enough 10 second-averaged velocities are available to calculate, with a reasonable degree of certainty, the statistics of the distribution of the downwind velocity components. The results from the past two summers presented in this thesis should be regarded as a preliminary investigation of some of the physical processes of air-sea interaction. By no means all the determining factors as yet have been successfully measured. At this stage a more thorough understanding of the behaviour of the instruments for measuring the transfer of momentum and a preliminary understanding of the physical processes involved has been gained.

Text

2011-10-31

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http://hdl.handle.net/2429/38440

Physics

University of British Columbia

Graduate