An Analytical Shelf-Ocean Coupled Model for the Bonney Coast Upwelling

An analytical shelf-ocean coupled model has been developed to study the upwelling system off the south-eastern part of South Australia (Bonney Coast). The shelf model is depth-integrated while the outer ocean has two layers of different water properties. It is assumed that the cold water comes from the bottom layer of the ocean model. When the shelf slope is of exponential form in the cross-shore distance, an analytical solution is obtainable. The two-layered ocean contains both barotropic and baroclinic modes, and allows an initial along-shore current in either layer. The shelf and the ocean are then coupled through continuity in both the surface elevation and cross-shore transport. The shelf width significantly affects the upwelling rate, with a smaller rate for a greater width. The upwelling rate is found to be directly proportional to the proximity of the cold water to the shelf head. Upwelling near the shelf break is reduced with an initial surface current flowing in the opposite direction to the upwelling favourable wind, and the reduction increases with the strength of the initial current. Although upwelling further off the shelf break is slightly increased, the reduction of the upwelling near the shelf break is more prominent when the upwelling favourable wind lasts for only a short time. An initial subsurface current flowing in the same direction as the upwelling favourable wind is seen to produce similar features. The above results are applicable to the upwelling system off the Bonney Coast where an upwelling favourable zone is observed in the region of a narrow shelf and a small initial current.