Laboratory Simulation of Tidal Rectification over Seamounts: Homogeneous Model

Abstract

The problem of the oscillatory motion of a homogeneous, rotating fluid in the vicinity of an isolated topographic feature is investigated in the laboratory and numerically. The laboratory experiments are conducted by fixing a cosine-squared body of revolution near the outer boundary of a circular tank rotating about a vertical axis with an angular velocity Ω(t)=Ω0+Ω1sin?t, where Ω0 is the mean background rotation and Ω0 and ? are the magnitude and frequency of an oscillatory component. Experiments with an oscillatory flow show clearly that a mean anticyclonic vortex is formed in the vicinity of the topographic feature. Surface floats are used to determine typical particle paths for various flow conditions and these are shown to vary markedly with the Rossby and temporal Rossby numbers of the background flow. Eulerian velocity profiles along and normal to the streamwise axis are used to quantify the anticyclonic vortex. A scaling analysis is advanced to show how the strength and distribution of the anticyclonic current varies with the various system parameters. The laboratory findings are in good agreement with the scaling analysis and with the theoretical model of Wright and Loder. A nonlinear numerical model, using the quasi-geostrophic potential vorticity equation, is considered; the results correlate well with the scaling analysis and the laboratory experiments. The laboratory and numerical experiments are used to estimate the magnitude of the mean anticyclonic motion that might be expected in the vicinity of Fieberling Guyot. Future laboratory and numerical experiments will consider the additional feature of background stratification.