Variability and forcing of the East Australian Current

The spatial and temporal variability of the East Australian Current (EAC) is investigated using 6 years (1993–1998) of surface geostrophic stream function from an optimal interpolation of altimeter sea surface heights and velocities derived from tracking thermal features in satellite imagery. Variability appears as a series of cyclones and anticyclones propagating southwestward and westward with periods between 90 and 180 days. The behavior of the variability changes over the 6 years. Energy in the mesoscale frequencies moves slowly south and diminishes with more westward propagation in the region where the current separates from the coast. We find no evidence for a consistent forcing of the EAC by mesoscale signals propagating westward from the South Pacific basin. We suggest that the observations are consistent with variability originating between 32°S and 35°S through intrinsic instabilities of the current.