Path and variability of the Agulhas Return Current

Olaf Boebel^1,2, Tom Rossby¹, Charlie Barron³, Johann Lutjeharms⁴ and Walter Zenk⁵

1)   Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA

2) now at Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

3) Naval Research Laboratory, Stennis Space Center, MS, USA

4) University of Cape Town, Cape Town, South Africa

5) Institut fuer Meereskunde an der Universitaet Kiel, Kiel, Germany

Abstract and Summary

This virtual poster presents the first (preliminary) analysis of direct velocity measurement in the Agulhas Retroflection Current (ARC) (see Intro) from float (RAFOS), acoustic Doppler current profiler (ADCP), and estimates of absolute steric sea surface height (MODAS SSH) data (see Data). The ARC's width is between 60 and 70 km, with peak velocities over 2 m/s near the surface. Transport in the upper 1350m was calculated to be around 61Sv (see Velocity). Analysis of absolute steric sea surface height data suggests that the current features at least three quasi-stable meanders, with troughs  at 26.8°, 32.6° and 38.9°E and crests at 29.7°, 35.5° and 42.9°E. North of the ARC, on its subtropical side, regular, seasonally locked shedding of cyclonic cold core eddies occurrs from the meander troughs. We observed near-simultaneous shedding from the second and third trough in austral fall, suggestive of a seasonal intensification of the Agulhas Current transport. The eddies migrated westward and merged with the trough located upstream from the shedding trough (see Dynamics). These findings are corroborated by a statistical comparision of the independent data sets MODAS SSH, ADCP and RAFOS floats. Both the RAFOS/MODAS and the ADCP/MODAS comparison have provided us with encouraging results. Correlation coefficients between 0.6 and 0.8 (see Statistics) suggest that MODAS is realistic enough to warrant an analysis of the MODAS field alone, in order to extract information on the 3 year mean path of the ARC and discuss its temporal evolution.