AGULHAS EDDIES - A SYNOPTIC VIEW USING GEOSAT ERM DATA

Warm core rings formed in the Agulhas Retroflection transfer water fro m the Indian Ocean to the South Atlantic. In an attempt to measure the strength of this exchange, a combination of satellite altimeter and h ydrographic data are used to examine Agulhas eddy paths and decay rate s in the South Atlantic, Because the surface dynamic height of a warm core eddy is higher than surrounding waters the rings are visible in s atellite altimeter measurements. Over 20 Agulhas eddies have been trac ked from maps of anomalous sea surface height (SSH) derived from the G eosat Exact Repeat Mission (ERM) dataset. The correlation (r(2)) of dy namic height referenced to 2000 dbar and anomaly SSH for one coinciden tally sampled area is 97% within an Agulhas eddy, dropping to a fracti on of that outside of it, indicating that the SSH anomaly signal is a reliable measure for strong features like Agulhas eddies. The sizes an d distribution of the Agulhas eddies in the ERM record compare favorab ly with those in recent hydrographic records From the area. individual eddy tracks from the ERM show the influence of topography, with slowe d translation over areas of steep relief. The eddies tracked take a ge nerally WNW course across the South Atlantic, propelled by the mean fl ow and internal dynamics. While propagating westward, Agulhas eddies d ecay in amplitude with an e-folding distance of O(1700-3000 km) alongt rack. As they approach the western boundary of the South Atlantic, at 40 degrees W, the eddies have O(10%) of their initial amplitude remain ing. This study finds the residence time of an Agulhas eddy in the Sou th Atlantic to be 3-4 years. On average, the authors find six eddies p er year form by the retroflection that enter the South Atlantic. The 2 0 eddies tracked therefore represent 50%-60% of the population that wo uld have been extant during the ERM. The Agulhas eddies appear to cont ribute a minimum of 5 X 10(6) m(3) s(-1) to the Indian-South Atlantic water mass transfer, with a corresponding energy flux on the order of 10(17) J.