25-Day Period Large-Scale Oscillations in the Argentine Basin Revealed by the TOPEX/Poseidon Altimeter

The measurement of the global sea surface height made by the TOPEX/Poseidon satellite has provided the first synoptic view of large-scale oceanic variability at intraseasonal scales from weeks to months. Areas of significant intraseasonal variability were found primarily in the Tropics and the high-latitude oceans, the Southern Ocean in particular. The focus of the paper is the finding of large-scale oscillations at a period of 25 days in the Argentine Basin of the South Atlantic Ocean. These oscillations exhibit a dipole pattern of counterclockwise rotational propagation centered at 45S, 317E over the Zapiola Rise. The scale of the dipole is about 1000 km. The peak-to-trough amplitude is on the order of 10 cm. The amplitude of these oscillations has large seasonalto-interannual variations. These oscillations are shown to be associated with a free barotropic mode of the basin as a solution to a linearized barotropic vorticity equation. Closed f/H contours provide a mechanism for the confinement of the waves to the topographic feature of the Zapiola Rise. Results from a numerical model simulation reproduced the patterns of the observed oscillations. The resultant mass transport variability is on the order of 50 Sv (Sv 10 6 m 3 s 1 ). Deep current meters in the Argentine Basin reveal signals consistent with the altimetry observations.