THE MESOSCALE STRUCTURE OF THE LEEUWIN CURRENT - A COMPARISON OF LABORATORY MODELS AND SATELLITE IMAGERY

Details of the mesoscale variability of the Leeuwin Current are determined from a study of NOAA satellite advanced very high resolution radiometer images over the period 1984-1985 for the area between Shark Bay and Cape Leeuwin on the west coast of Australia. At most times during the selected period there are large wavelike protrusions along the current. During at least three separate periods these appear as a set of three or four roughly equally spaced meanders, or wave crests. Each meander diverts the warm water far offshore of the shelf break, where the core of the southward current is otherwise normally found. Their amplitude generally grows in time, and the anticyclonic motions in the meanders are usually accompanied by cool cyclonic circulations between the meanders. Large meanders are more than 200 km across. Although the flow is unsteady and fronts sometimes translate at speeds of up to 0.8 m s-1, the meanders do not move along the coast and can be followed through the images for 30 to 60 days. These features represent very major diversions to the southward flow in the Leeuwin Current and result in large fluctuations in local current velocity and sea surface temperature. On this scale, the structure of the flow has many features in common with that observed in laboratory experiments with coastal currents driven by steady thermal forcing. Smaller billow structures are also apparent along the strongest temperature fronts in the satellite images.