Submesoscale Frontal Vortices and Eddies along the East Australian Current observed by HF Radars

The East Australian Current (EAC) is the major feature of the ocean circulation along south-eastern Australia, influencing the shelf circulation, water temperature, phytoplankton to fish distribution and abundance and the regional climate. While the shedding of mesoscale warm core eddies at the EAC separation of the coast is relatively well understood, little is known about its sub-mesoscale frontal instabilities.

More than 1 year of surface currents from HF Radars, in conjunction with mooring measurements, satellite sea surface temperature and ocean color, highlight for the first time the occurrence and propagation of meanders along the inshore edge of the EAC. These instabilities are mostly barotropic and migrate poleward as far as 500 km south, with advection speeds of ~0.3 m/s. Investigation into the flow field kinematics shows high Rossby numbers and a strong impact on horizontal divergence and particle dispersion. Wind stress appears to influence the fate of these ageostrophic meanders, their growth and potential evolution into cyclonic cold core eddies. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal waters, impacting physical and biological connectivity over large distances.