NUMERICAL-STUDIES OF SMALL ISLAND WAKES IN THE OCEAN

Two and three-dimensional oceanic flows around small islands patterned after Barbados, W.I. (13 degrees 10' N latitude: 59 degrees 30' W lon gitude) were modeled numerically to investigate island wake effects. T he two-dimensional simulations closely agreed with laboratory flows, f or both attached and shedding wake regimes. As expected, results for a flat bottom confirmed that the Coriolis terms strongly affect pressur e but not the flow. For idealized, yet typical incident dow speeds, wa ter column stratification, island topography and appropriate Coriolis terms, three-dimensional simulations readily produced elongated wake p atterns, dominated by surface intensified von Karman-like vortices. Ef fects of grid resolution, viscosity, bathymetry, and Coriolis forces o n wake characteristics were studied. For islands with typical bottom s lopes, realistically small horizontal eddy diffusivity has a minor eff ect compared to bottom drag in generating vorticity. Near-shore bathym etry (viz., the absence or presence of a continental shelf surrounding the island) plays a major role in determining the scale, intensity, a nd shedding period of the vortices. The addition of a 15 km wide conti nental shelf around the island increased the shedding period by 67%, w hile reducing the Coriolis force by 50% reduced the period by only 14% . Although observational data is sparse, inferred flow patterns do sho w von Karman-like structures near Barbados, even if eddies are not loc ated exactly as expected. The numerical computations demonstrate that shedding eddy wakes are easily generated, and lend encouragement to th e further search for organized wakes downstream of the island.