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

Dominant spatio-temporal 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 a r e isolated ranging from the quasi-biennial to the quasi-decadal. Two quasi-biennial bands are centered around 2.2 and 2.7-year periods; two interannual bands a r e centered around 3.5 and 4.4-year periods; the fifth band at the quasi-decadal frequency is centered around 11.4-year period. Between 1920 and 1955, t h e quasi-decadal band is less prominent compared to the quasi-biennial bands. This happens to be the period when SLP gradually increased over the GreenlandIceland regions. The spatial pattern at the quasi-decadal frequency displays a n 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, creates the impression 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 NAO and are associated with tropical Atlantic Ocean warming (cooling) with different spatial evolution. The two interannual bands show opposite SST evolution to t h e south of the ITCZ i.e.; southeastward evolution from the western tropical Atlantic for the 3.5-year period and westward spreading from the eastern tropical Atlantic for the 4.4-year period. Moreover, a significant coherence (with a one year phase lag) is found between the SST time series along the equatorial Atlantic obtained from the 3.5-year period, and the SST time series in the NIÑO3 area in the Pacific. It is cautiously argued that the 3.5-year period is largely associated with the global El Niño Southern Oscillation (ENSO) phenomenon, while the evolution of the 4.4-year period depends more upon Atlantic local conditions.