Topographically generated eddies

Abstract

The interaction between temporally varying currents and the bottom topography of the ocean is investigated by the numerical and analytic examination of the following simple model. The flow of an inviscid, stratified fluid is initiated from relative rest in a uniformly rotating system containing an isolated topographic feature. The evolution of the flow redistributes vorticity and temperature in such a way that relatively cold water with anticyclonic vorticity exists over the topographic feature, while water shed from above the topographic feature sinks, thereby inducing a warm anomaly with cyclonic vorticity. For sufficiently strong oncoming flows, the shed fluid continually drifts downstream in the form of a relatively warm eddy. If the oncoming flow is relatively weak, the interaction between the anticyclonic and cyclonic vorticity distributions traps the warm eddy and it remains in the vicinity of the topographic feature.

We suggest that recent observations of an eddy in the vicinity of the Atlantis II Seamount and the existence of the large amount of high frequency energy near the bottom of the ocean measured by the MODE experiment may be partly explained in terms of the above mechanism. We conclude by speculating that vorticity redistribution by topography may be a contributing factor to cyclogenesis in the atmosphere.