Satellite images of an unstable warm eddy derived from the Leeuwin Current

Abstract Satellite images from the AVHRR (Advanced Very High Resolution Radiometer) on NOAA7 reveal a warm eddy in the Southern Ocean approximately 300 km south of the Australian coast in spring of 1982. The eddy, which we believe originated at the edge of the Leeuwin Current, was slightly elongated in shape with two arms of warm water stretching outward in a spiral appearance, a structure seen in previous laboratory experiments with unstable baroclinic eddies. The sea surface temperature difference, radius and estimated depth of the eddy imply a rotating Froude number close to or slightly greater than a critical value that was determined for the onset of baroclinic instability of laboratory vortices. We suggest that the observed eddy was in the process of decay via a similar instability.