Relationship between zonal and meridional modes in the tropical Atlantic

The tropical Atlantic displays two main modes of variability; the meridional or dipole mode and the equatorial zonal mode. It was proposed recently, that these two modes are correlated and are both forced within the tropics by latitudinal displacements of the ITCZ. This modeling study shows that while the two modes are correlated for limited record lengths prior to and after 1976, the correlation falls apart when longer time-series from 1949 to 2000 are considered. The 1976 'climate shift' also occurred in the tropical Atlantic seen as a thermocline shift similar to the Pacific, forced dynamically within the tropics. The first EOF of the simulated thermocline depth captures the interdecadal mode with the 1976 shift. The first EOF of SST anomalies prior to (after) 1976 represents the meridional (zonal) mode, consistent with the previous finding that the relation between the eastern Pacific and Atlantic ITCZ is stronger in the 1980-90's.