Modes of mesoscale sea surface height and temperature variability in the East Australian Current

Abstract

Mesoscale variability where the East Australian Current (EAC) separates from the coast is studied using sea surface temperature and surface velocity streamfunction observed by satellite and a regional numerical model. The mean circulation simulated by the model (the Regional Ocean Modeling System (ROMS)) is compared to a high‐resolution regional climatology, and the realism of the simulated mesoscale variability is tested by comparison to statistical analyses of the satellite data. Both ROMS and data show spectral peaks in the mesoscale energy band at periods between 90 and 180 days. Complex Empirical Orthogonal Function (EOF) analysis identifies two significant modes of mesoscale variability in the data; an Eddy Mode, for which the variability propagates southwestward along the coast, and a Wave Mode, for which phase propagation is predominantly onshore. The regional model open boundary conditions include only annual and semiannual harmonics of variability so remote mesoscale forcing is absent. The Eddy Mode is represented well in the model indicating this aspect of the circulation results from local instabilities of the flow and that its underlying dynamical process is simulated well. While the observed and modeled Wave Modes have some similarities, their differences suggest the model is deficient in representing westward propagation of mesoscale period variability in the region. Whatever the source of this energy, the orthogonality property of the EOF analysis indicates the Wave Mode does not interact significantly with eddy processes in the EAC separation.