The western Equatorial Undercurrent (EUC) and North Equatorial Countercurrent (NECC) are investigated at 38°W using contemporaneous subsurface (ADCP) and high-resolution near-surface (drifters + satellite altimeter) velocity measurements, together with hydrographic (CTDO2) data that were collected from 1998 to 2006. The observations reveal an EUC with a strong semiannual pattern of intensification. Direct measurements also confirm the existence of a northern branch of the NECC (nNECC), observed here for the first time in the western tropical Atlantic. The NECC displays an annual cycle of northward migration on the basin, driven by the Sverdrup transport generated by the wind field. In this cycle the nNECC is a semipersistent feature fed by waters from the Northern Hemisphere and the residual nNECC flow from the previous year.
Citation: Urbano, D. F., R. A. F. De Almeida, and P. Nobre (2008), Equatorial Undercurrent and North Equatorial Countercurrent at 38°W: A new perspective from direct velocity data, J. Geophys. Res., 113, C04041, doi:10.1029/2007JC004215.
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The temporal evolution of the coupled variability between the South Atlantic Convergence Zone (SACZ) and the underlying sea surface temperature (SST) during austral summer is investigated using monthly data from the NCEP/NCAR reanalysis. A maximum covariance analysis shows that the SACZ is intensified [weakened] by warm [cold] SST anomalies in the beginning of summer, drifting northward. This migration is accompanied by the cooling [warming] of the original oceanic anomalies. The results confirm earlier analyses using numerical models that suggest the existence of a negative feedback between the SACZ and the underlying South Atlantic SST field. A linear regression of daily anomalies of SST and omega at 500 hPa to the equations of a stochastic oscillator reveals a negative ocean–atmosphere feedback in the western South Atlantic, stronger during January and February directly underneath the oceanic band of the SACZ.
Citation: De Almeida, R. A. F., P. Nobre, R. J. Haarsma, and E. J. D. Campos (2007), Negative ocean-atmosphere feedback in the South Atlantic Convergence Zone, Geophys. Res. Lett., 34, L18809, doi:10.1029/2007GL030401.
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