Comparisons between Surface, Barotropic and Abyssal Flows during the Passage of a Warm-core Ring

A comparison is made of results for barotropic, surface and abyssal flows during the formation and passage of a warm-core ring in the East Australian Current. The barotropic velocities are estimated from sea-floor measurements of the horizontal electric field, which is induced by water motion. Values for the surface and near-bottom velocities are obtained generally by more traditional methods. A strong similarity is observed between the directions of the barotropic and surface flows. At a site close to the foot of the continental slope, the barotropic and near-bottom velocities are also similar, both in direction and magnitude. A possible explanation for this effect is that proximity to the coast constrains flow directions and causes the streamlines at depth to converge on the western (or near-shore) side of the warm-core ring. The determination of barotropic velocities enables barotropic volume transports to be estimated and compared with traditional geostrophic volume transports calculated for water motion between the surface and a depth of 1300 m. The barotropic transports are found to be greater than the geostrophic transports by a factor of approximately 1.6, indicating the significance of deep-water flow in the East Australian Current.