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Low frequency current oscillations and topographic waves in the Strait of Georgia

University of British Columbia

Chang (1976, see also Chang, Tabata, and Pond, 1976) has shown that up to 46% of the kinetic energy associated with horizontal motions in the Strait of Georgia, British Columbia, is contained in broad-banded, low-frequency current oscillations characterised by periods ranging from 4 to over 100 days. The purpose of this thesis is to present a simple dynamical model which may provide a partial explanation of these oscillations. The Strait of Georgia is modelled by an infinitely long, rectangular channel with a bottom that slopes upward to the east. Two choices of the density stratification are studied: (1) a two-layer system and, (2) a system with constant Brunt-Väisälä frequency. Both models admit northward-travelling topographic planetary waves with periods that lie in the observed range. However these models do not accurately predict the vertical distribution of horizontal kinetic energy. In addition several general theorems regarding phase and energy propagation and the vertical structure of these waves in a system with arbitrary continuous stratification are proven. In particular it is shown that both phase and energy propagate northward, and that in a stably stratified system the wave amplitude increases with depth.

Text

2010-02-16

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http://hdl.handle.net/2429/20306

Oceanography

University of British Columbia

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