SIMPLE CLIMATIC INDEXES FOR THE TROPICAL ATLANTIC-OCEAN AND SOME APPLICATIONS

Two indices related to the sea surface temperature (SST) variability in the tropical Atlantic are proposed. One index describes the SST averaged over the whole basin (30-degrees-N to 20-degrees-S, 60-degrees-W to 15-degrees-E), and the other illustrates a meridional dipole between the northern and southern hemispheres. The computational method for obtaining these indices is intentionally kept simple, the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses. Monthly time series for both indices are produced from 1964 up to the present time. The whole basin index exhibits principally a sustained warning which has intensified since about 1975, and it has a significant periodicity close to that of the quasi-biennial oscillation. The dipole index exhibits a decadal-scale variation, and its building up seems to be related to other worldwide climatic changes, as for instance El Nino / Southern Oscillation extreme episodes, rainfall variabilities over the Brazilian Nordeste and African Sahel.