OC4331-Mesoscale Oceanography
Final Project Summary

The East Australian Current

Project Team Member

LEUT Steve Wall, RAN

The East Australian Current (EAC) is the poleward flowing Western Boundary Current (WBC) of the South Pacific Gyre and is related to other WBCs such as the Gulf Stream (North Atlantic), Kuroshio (North Pacific) and the Agulhas (South Indian).  The source of the EAC is the warm tropical water of the South Pacific, that has a temperature of around 29-310C, and is around one metre higher than the cooler waters of the Tasman Sea to the south. 

The EAC volume transport is highly variable, from as low as 15Sv to around 30Sv, with the highest volumes during the austral winter.  This variability is attributable to the relative strength of trade wind regime in the South Pacific which is greatest in winter (or sub tropical dry season) and weakest in summer (or sub tropical wet season). Some of the characteristics of the EAC are as follows:                 

  • Mean depth ~ 500m
  • Mean width ~ 100km
  • Mean velocity ~ 2-3kts 
  • Max velocity ~ 7kts

The EAC generates warm cored anti-cyclonic eddies in the Tasman Sea that are up to 200km in diameter and 1000m deep and can remain intact for up to one year.  The EAC flows poleward along the coast and continental shelf from around 150S and separates from the central eastern coast of Australia between 30-330S forming a sharp front in velocity and temperature as it turns eastward, where a temperature front of up to 70C have been observed.  The existence of smaller cyclonic eddies and vortices is evident where the EAC interacts with coast and models have shown that these eddies may be advected with the large scale anti-cyclonic eddies and become ‘parasitic’ in nature.

The Royal Australian Navy’s  (RAN) Fleet Weather and Oceanography Centre (FWOC) uses altimetry and SST imagery to construct a weekly oceanographic summary of the separation of the EAC from the coast and the position, strength and movement of the warm cored eddies as they separate from the EAC and move poleward along the east coast.


Figure 1. A view of the surface current system around Australia.

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Figure 2. A more detailed view of the EAC and its subsidiary currents.

References

CSIRO Marine Research http://www.marine.csiro.au/LeafletsFolder/37eac/

Bowman M.J., D.E. Dietrich and B.G. Sanderson. Non linear interactions of East Australian Current eddies. In: Oceanic Fronts and Related Phenomena: Konstantin Fedorov International Memorial Symposium. UNESCO Intergovernmental Oceanographic Commission Workshop Report No. 159, pp. 48-53 (2000).

M Roughan and J H. Middleton, “On the East Australian Current: Variability, encroachment, and upwelling” (2004). Journal of Geophysical Research-Oceans. 109 (C7), Article 10.1029/2003JC001833.

 

Mata, M. M., S. E. Wijffels, J. A. Church, and M. Tomczak (2006), Eddy shedding and energy conversions in the East Australian Current, J. Geophys. Res., 111, C09034, doi:10.1029/2006JC003592.

 

Nilsson, C.S., and G.R. Cresswell, 1981: The formation and evolution of East Australia Current warm-core eddies. Prog. Oceanog. , 9, 133-183.

 

Cresswell, G.R., and R. Legeckis, 1986: Eddies off southeastern Australia. Deep-Sea Res. , 33, 1527-1562.

 

 

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