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Modelling of the circulation of northern British Columbia waters

University of British Columbia

A numerical model is used to improve our understanding of the mean circulation of northern British Columbia waters. The velocity field arising from tidal, wind, river runoff, and baroclinic effects is studied and the influence of the earth's rotation investigated. The model is three-dimensional, diagnostic, nonlinear through tidal forcing, and uses finite element techniques. The grid has linear horizontal triangular elements with vertical sigma levels. The model output is a linear combination of the currents obtained under the individual forcings. In this thesis, the model has been modified in order to improve the parameterization of friction processes, to add the vertical advection of tidal momentum by the tides, and to include the stratification effect on eddy viscosity. A major circulation feature is a large cyclonic eddy covering the central-eastern Dixon Entrance. This eddy, referred as the Rose Spit Eddy, is actually simulated by a combination of two or three smaller gyres, which seasonally vary in size and intensity. The modeled eddy is, in good agreement with observations, characterized by a rotation period of 3 to 40 days, depending on the season and the initial distance of the numerical particle from the center of the gyres. This eddy persists in all seasons but occasionally disappears. A disappearance occurred, consistent with current observations, in October 1984. The Learmonth Bank Gyre, an anticyclonic eddy located in western Dixon Entrance, is also simulated by the model. Baroclinicity and tidal rectification, respectively responsible for the generation of the Rose Spit Eddy and Learmonth Bank Gyre, are the dominant effects in the study region. The earth's rotation, necessary for the formation of those two eddying motions, as well as the vertical advection of tidal momentum were found to be essential to bring the current speeds closer to the observed values. The effect of stratification on the residual currents, through turbulence reduction, was found to be negligible.

Thesis/Dissertation

application/pdf

2009-04-01

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http://hdl.handle.net/2429/6696

Oceanography

University of British Columbia

UBCV

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