Evidence of a relationship between the two main types of interannual climatic variability over the tropical Atlantic

The tropical Atlantic Ocean has two main types of interannual climate variability: an equatorial and a meridional type, also known as the dipole-type, which does not seem to have a counterpart in the Pacific. The equatorial type is primarily a mixed-layer phenomenon. It is responsible for the warm land cold) sea surface temperature (SST) events and is associated with the thermocline slope displacements arising from wind-forced equatorial adjustment. The dynamics associated with this first type is very similar to the Pacific Ocean El Nino phenomenon. The second type encompasses the whole tropical basin and is characterized by a north-south oscillation of basin-scale SST. The two parts of the Atlantic dipole-type are separated by the mean position of the intertropical convergence zone (ITCZ). To date, this type has been observed tin the ocean) only from SST fields. In this study it has been shown via a multi-year oceanic general circulation model, and by direct surface and subsurface thermic observations, that these two types of climatic variability appear to be well related statistically. The study period ranges from 1985-1993. The results suggest that the physics of the interannual variability for these two types is the same as the annual variability with respect to their relationship to the north-south displacements of the ITCZ. ((C) Academie des sciences/ Elsevier, Paris.)