Three Agulhas rings observed during the Benguela Current experiment

A field program to study the circulation of the Benguela Current and its extension into the southeastern Atlantic Ocean has completed the survey and instrument deployment phase. We report here new observations of three Agulhas rings north and west of Cape Town, South Africa. Three mesoscale anticyclonic rings initially identified by means of TOPEX/POSEIDON altimetry were surveyed with expendable bathythermographs, conductivity-temperature-depth-oxygen profiles, direct current measurements from a lowered acoustic Doppler current profiler, a hull-mounted acoustic Doppler current profiler, and satellite-tracked surface drifters. Characteristics of the rings are presented, and their origins are discussed. Two are typical Agulhas rings surveyed at different times after their generation; the third Agulhas ring has an anomalous water mass structure whose most likely origin is the Subtropical Front.