Empirical orthogonal function analyses of tropical Atlantic sea surface temperature and wind stress: 1964–1979

Abstract

Scalar and vector empirical orthogonal function (EOF) analyses have been performed on monthly sea surface temperature (SST) and wind stress within the tropical Atlantic region for the years 1964–1979. The long‐term average was subtracted from the 16‐year SST and wind stress monthly fields to focus on the seasonal variability and its interannual modulations. A smaller cumulative percent of variance accounted for by the first eigenvectors of wind stress reflects the greater variability of the wind than that of SST. Analysis of regional seasonal SST events requires a combination of the first three EOFs, whereas the dominant events of the seasonal cycle of the wind stress are adequately represented by E1 and E2. As in the Pacific, an increase of the trade wind system is observed between the 1960s and the 1970s. Our analyses provide diagnostic insight into two types of large spacetime scale episodes. The first type is exemplified by the following sets of observations: during the spring of 1968 (spring 1976), an abnormal relaxation (intensification) of the wind stress occurred in both the northeasterlies and the southeasterlies. Subsequently, equatorially trapped anomalous warming (cooling) occurred inside the Gulf of Guinea. The second type is exemplified by the following: during 1972 to 1975, the northeasterlies (stronger) and the southeasterlies (weaker) acted out of phase, leading to a more global response of the ocean. The oceanic response was different in the northern (colder) and southern (warmer) basins.