Propagation of the sea-surface temperature anomalies in the Tropical Atlantic

The evolving modes of the sea-surface temperature (SST) in the Tropical Atlantic on the short interannual (IA) timescale were obtained by performing the extended empirical orthogonal function (EEOF) analyses on this variable separately for the 106-year (1871–1976) and 20-year (1881–1900; 1901–1920; 1921–1940; 1941–1960) periods. The equatorial and inter-hemispheric patterns manifest in the first EEOF mode of each analysis as part of the short IA evolution of the SST anomalies in the Tropical Atlantic. Another outstanding feature of the first EEOF mode of each analysis concerns the propagations of the SST anomalies in the meridional direction within the 20° N–20° S band and in the zonal direction in the sector 40° W–20° W. For all analyses, the SST anomalies propagate northward from the equator to 15° N and southward from 20° N to 15° N, with the same sign anomalies merging approximately at 15° N. On the other hand, the SST anomalies propagate westward in the sector 40° W–20° W with a propagation rate close to that of the phase speed of the fastest baroclinic Rossby wave in the ocean. So, the observed propagations of the SST anomalies in the 20° N–20° S band might result from the combined effect of the surface oceanic currents in this band and the baroclinic Rossby waves in the ocean.