Decadal and Interannual SST Variability in the Tropical Atlantic Ocean

Abstract

The mechanisms regulating interannual and decadal variations of sea surface temperature (SST) in the tropical Atlantic are examined. Observed variations of sea surface temperature are typically in the range of 0.3°–0.5°C and are linked to fluctuations in rainfall on both the African and South American continents. The authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960–1989. Based on the results, experiments are conducted to determine the relative importance of heat flux and momentum forcing. Two dominant timescales for variability of SST are identified: a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for SST anomalies off the equator and an equatorial mode with a timescale of 2–5 years that is dominated by dynamical processes. The interhemispheric gradient of anomalous SST (the SST dipole) is primarily linked to the former process and thus results from the gradual strengthening and weakening of the trade wind system of the two hemispheres.