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 vari ability 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 i s the finding of large-scale oscillations at a period of 25 days in the Arg entine Basin of the South Atlantic Ocean. These oscillations exhibit a dipo le pattern of counterclockwise rotational propagation centered at 45 degree sS, 317 degreesE over the Zapiola Rise. The scale of the dipole is about 10 00 km. The peak-to-trough amplitude is on the order of 10 cm. The amplitude of these oscillations has large seasonal-to-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 top ographic feature of the Zapiola Rise. Results from a numerical model simula tion reproduced the patterns of the observed oscillations. The resultant ma ss 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 t he altimetry observations.