UBC Theses and Dissertations
Tidal residual circulation over an axisymmetric seamount : seamount geometry effects Shore, Jennifer A.
A numerical tidal model is used to investigate the effect of seamount geometry on tidally rectified residual flow and the resultant particle behaviour. A weakly nonlinear analytical solution of barotropic oscillatory flow over a tall, axisymmetric, isolated seamount is derived and compared to a numerical tidal model solution. The comparison is formulated for a flat topped seamount with parabolic sides and with a standing wave boundary condition that makes the problem analytically tractable and reduces it to a series of ordinary differential equations. Based on the model comparisons, it is concluded that the numerical model gives reasonable solutions for tall topographies. Comparisons to a Gaussian seamount and Kelvin wave forcing illustrate the generality of the results. Residual velocities axe found to be proportional to the aspect ratio of the topography showing that for cases where the deep water depth does not change, wider seamounts will tend to have weaker residuals. Numerical experiments are conducted to investigate the effect of changes in seamount base width, slope and height on the tidal residual field and particle behaviour. Consistent with the analytic solution, results show that as the seamount widens (with its percentage depth remaining unchanged) the magnitude of the maximum residual velocity decreases. Unlike previous results of other researchers, it was found that an increase in slope does not necessarily generate a strengthening of the maximum residual. Results from the particle tracking studies show, in part, that trapping is more sensitive to changes in distances to the shelfbreak than to changes in the base width. Furthermore, retention times are enhanced, more by increases in the flank slope than by increases in base width, or seamount height.
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