Dominant Patterns of Climate Variability in the Atlantic Ocean during the Last 136 Years

Dominant spatiotemporal patterns of joint sea surface temperature (SST) and sea level pressure (SLP) variability in the Atlantic Ocean are identified using a multivariate frequency domain analysis. Five significant frequency bands are isolated ranging from the quasi biennial to the quasi decadal. Two quasi-biennial bands are centered around 2.2- and 2.7-yr periods; two interannual bands are centered around 3.5- and 4.4-yr periods; the fifth band at the quasi-decadal frequency is centered around 11.4-yr period. Between 1920 and 1955, the quasi-decadal band is less prominent compared to the quasi-biennial bands. This happens to be the period when SLP gradually increased over the Greenland–Iceland regions. The spatial pattern at the quasi-decadal frequency displays an out-of-phase relationship in the SLP in the vicinity of the subtropical anticyclones in both hemispheres (indicative of an out-of-phase quasi-decadal variability in the North and South Atlantic Hadley circulation). The quasi-decadal frequency also displays an out-of-phase relationship in the SSTs north and south of the mean position of the intertropical convergence zone (ITCZ). This short-lived structure, lasting for approximately two years, supports the argument that a tropical SST dipole pattern is one of the characteristics of the quasi-decadal signal. All five frequency bands represent to some extent fluctuations of the North Atlantic oscillation and are associated with tropical Atlantic Ocean warming (cooling) with different spatial evolution. The two interannual bands show opposite SST evolution to the south of the ITCZ, that is, southeastward evolution from the western tropical Atlantic for the 3.5-yr period and westward spreading from the eastern tropical Atlantic for the 4.4-yr period. Moreover, a significant coherence (with a 1-yr phase lag) is found between the SST time series along the equatorial Atlantic obtained from the 3.5-yr period, and the SST time series in the NINO3 area in the Pacific. It is cautiously argued that the 3.5-yr period is largely associated with the global El Niño–Southern Oscillation phenomenon, while the evolution of the 4.4-yr period depends more upon Atlantic local conditions.