Circulation around Islands and Ridges
I am studying the influences of planetary scale topographic features such as islands and abyssal ridges on the mean and low frequency variability of the large scale circulation using both numerical models and simple theories. The circulation integral around an island places a strong constraint on the properties of the flow, both in the vicinity of the island and in the adjacent basins. Single islands or island chains allow for the passage of some forms of low frequency variability quite freely, while other forms are entirely blocked by the topography. Interesting circulation features arise in the mean flow, such as recirculation gyres, jets, and eastern boundary currents as a result of circulation constraints around the topography.
Although most recent efforts have been directed towards understanding the large-scale wind-forced circulation around islands, buoyancy-forcing can also alter the exchange between adjacent basins, particularly if it is concentrated along the western coast of the island or ridge. Diapycnal mixing near a boundary can result in significant dissipation, which results in a pressure drop along the boundary near the mixing region. This pressure drop must be balanced elsewhere along the island perimeter, giving rise to the possibility that diapycnal mixing, due either to air-sea exchange or internal wave breaking, can drive a large-scale circulations around topographic features that may extend far from the region of mixing.
This work has been generously supported through grants from the National Science Foundation and the Office of Naval Research.