A process-oriented numerical study of currents, eddies and meanders in the Leeuwin Current System

Abstract

While observations provide insight for the basic nature of features in the Leeuwin Current System (LCS), processoriented studies are useful for systematically investigating the characteristics and dynamical forcing mechanisms for the currents and eddies in the LCS. This process-oriented numerical study investigates the roles of wind forcing, thermohaline gradients and bottom topography on currents and eddy generation in the LCS with a terrain-following primitive equation model, in this case the Princeton Ocean Model (POM), on a beta-plane off the western and southwestern coast of Australia. Results show that the LCS is an anomalous Eastern Boundary Current that generates a surface poleward current predominantly over the shelf break, an equatorward surface current with upwelling next to the coast in localized regions, an equatorward undercurrent, and highly energetic mesoscale features such as meanders and eddies. Thermohaline gradient effects are shown to be the primary mechanism in the generation of a poleward (equatorward) current (undercurrent), eddies and meanders in the LCS. Inshore of the poleward surface flow, next to the coast, wind forcing plays an important role in generating an equatorward coastal current and upwelling. The major role of the wind is to slow the poleward surface flow, enhance eddy spin up and create localized upwelling regions, such as in the north near Shark Bay and just north of Cape Leeuwin. Bottom topography is shown to be an important mechanism for intensifying and trapping currents near the coast, weakening subsurface currents and intensifying eddies off capes. The surface poleward current is predominantly steered by the shelf break, frequently leaving the coast as it follows the 200-m depth contour southward to Cape Leeuwin and eastward into the Great Australian Bight. Overall, the results of this process-oriented study compare well with available observations in the LCS.