| Summary: | The interannual variability of the sea surface temperature (SST) in the western South Atlantic Ocean is explored by applying the composite analysis method to a 40-year period of COADS data (1953-1992). Interactions between the ocean and the overlying atmosphere, as well as oceanic processes, are investigated in order to explain the variability in the SST associated with the two converging western boundary currents in this region: the Brazil and the Malvinas Currents. The pattern of interannual variability of SST displays a dipole-like structure in the vicinity of the confluence of the two currents. That is, the SST fluctuations in both currents are roughly out-of-phase: warm episodes in one current accompany cold episodes in the other. It is suggested that the variability in the oceanic advection of the currents accounts for part of the observed variability in SST in the confluence region, the dipole pattern being associated with the strength of the temperature gradient in the confluence. The pattern of variability of the air-sea heat exchange associated with the observed SST fluctuations displays a distribution of ocean-to-atmosphere flux anomalies roughly out-of-phase with those of SST. It is concluded that the SST fluctuations associated with the Brazil and Malvinas Currents are related to the variability in both the air-sea heat exchange and the oceanic advection of the currents. The warm and cold events observed in the currents are associated with distinct atmospheric circulation patterns. Thus, it is suggested that changes in the atmospheric circulation on interannual timescales induce anomalies in the air-sea heat exchange, which have been found to be partly responsible for the variability in SST of the Brazil and Malvinas Currents.
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