Ocean observations show cyclonic eddies intensify internal tides off eastern Australia

Eduardo Queiroz1, Moninya Roughan2, Colette Gabrielle Kerry3 and Shane R Keating1, (1)University of New South Wales, Sydney, NSW, Australia, (2)University of New South Wales, Biological Earth and Environmental Sciences, UNSW Sydney, NSW, Australia, (3)University of New South Wales, Coastal and Regional Oceanography Lab, School of Biological Earth and Environmental Sciences, UNSW, Sydney, NSW, Australia
Abstract:
Internal tides can generate ocean mixing, surface convergences and near-bottom currents, so their predictability is of interest. The interaction between internal tides and mesoscale ocean features makes their prediction challenging. Using in situ observations of temperature, salinity and velocities from an array of deep ocean moorings, this study characterises the strength and variability of the internal tides, in both time and space, off eastern Australia (~ 27° S). The internal tide energy in the diurnal frequency band is, generally, greater than in the semidiurnal band. Internal tide variability is compared to local barotropic tidal forcing, stratification, sea surface density and eddy kinetic energy to determine the influence and interaction with mesoscale ocean circulation. The results reveal that the diurnal internal tide can be locally generated above the continental slope and the strength is modulated by the passing of mesoscale cyclonic eddies that alter the local stratification and velocity field. Peaks in semidiurnal internal tide energy are sporadic and may result from a combination of remote and local generation. The results provide insight into the origin of the internal tides above the continental slope and the mechanisms of variability. Studying the characteristics of internal tides and their interaction with ocean features helps us quantify their variability and improve their predictability, which is non-trivial in contrast to the deterministic barotropic tides that generate them.