Numerical Studies of Flow Past Isolated Seamounts.

Our long-range goal was to understand the influence of tall and/or steep topographic features on the ocean circulation. Of particular interest was the occurrence of systematic processes such as upwelling, mixing, eddy shedding, mean flow generation, and the trapping of energy and/or water parcels in the neighborhood of such features. Our approach was to use a sigma-coordinate primitive-equation numerical model to explore the flow past a tall isolated seamount under a variety of conditions, and with varying degrees of realism. We began with several idealized studies of flow past a tall isolated seamount. A number of technical issues were explored in order to better understand the model performance and limitations, as well as to provide insight into model improvements (Beckmann and Haidvogel, 1993). We studied eddy shedding and the formation of regions of trapped fluid, called Taylor caps, resulting from steady flow past a tall, Gaussian-shaped seamount in a stratified ocean (Chapman and Haidvogel, 1992). We quantified the occurrence of Taylor caps for various inflow speeds and seamount heights. We then investigated the generation of internal lee waves over this same idealized seamount, showing that these lee waves result from the local nonlinear acceleration of flow around the seamount, and that they may be important for local mixing (Chapman and Haidvogel, 1993). We also studied the excitation of seamount-trapped waves caused by weak ambient tidal oscillations (Haidvogel et al., 1993). This work confirmed the amplification of these waves under certain conditions and showed that a rectified mean anti-cyclonic flow is generated as well, consistent with observations near Fieberling Guyot.