A numerical modeling study of the East Australian Current encircling and overwashing a warm-core eddy

[1] Warm-core eddies (WCEs) often form in the meanders of Western Boundary Currents (WBCs). WCEs are frequently overwashed with less dense waters sourced from the WBC. We use the Regional Ocean Modelling System to investigate the ocean state during the overwashing of one such WCE in October 2008 in the East Australian Current (EAC). Comparisons of model outputs with satellite sea surface temperature and vertical profiles show that the model provides a realistic simulation of the eddy during the period when the EAC encircled and then overwashed the eddy. During the encircling stage, an eddy with closed circulation persisted at depth. In the surface EAC water entered from the north, encircled the eddy and exited to the east. The overwashing stage was initiated by the expulsion of cyclonic vorticity. For the following 8 days after the expulsion, waters from the EAC washed over the top of the eddy, transferring heat and anticyclonic vorticity radially-inward. After approximately one rotation period of overwashing, the eddy separated. The overwashing creates a two-layer system that forms a subsurface maximum velocity at the interface of the two layers. Analysis of water mass properties, Eulerian tracer dynamics, and Lagrangian particle tracks show that the original eddy sinks 10-50 m during the overwashing period. Overwashing has been observed in many WBCs and occurs in most WCEs in the western Tasman Sea.