Relationship between zonal and meridional modes in the tropical Atlantic

The tropical Atlantic displays two main modes of variability; the meridiona l or dipole mode and the equatorial zonal mode. It was proposed recently, t hat these two modes are correlated and are both forced within the tropics b y latitudinal displacements of the ITCZ. This modeling study shows that whi le the two modes are correlated for limited record lengths prior to and aft er 1976, the correlation falls apart when longer time-series from 1949 to 2 000 are considered. The 1976 'climate shift' also occurred in the tropical Atlantic seen as a thermocline shift similar to the Pacific, forced dynamic ally within the tropics. The first EOF of the simulated thermocline depth c aptures the interdecadal mode with the 1976 shift. The first EOF of SST ano malies prior to (after) 1976 represents the meridional (zonal) mode, consis tent with the previous finding that the relation between the eastern Pacifi c and Atlantic ITCZ is stronger in the 1980-90's.