Global Modes of ENSO and Non-ENSO Sea Surface Temperature Variability and Their Associations with Climate

In this chapter we review much of the recent work by others regarding the nature of the global modes of sea surface temperature (SST) variability and the SST involvement in interannual to multidecadal climate variability. We also perform our own analysis of global SST so as to describe the SST variability associated with El Niño/Southern Oscillation (ENSO) and the low-frequency modes not associated with ENSO (non-ENSO). ENSO is a global phenomenon with significant phase propagation between basins, which we preserve and describe using complex multivariate analysis and subsequently remove from the global SST data. A similar analysis of the residuals reveals three non- ENSO modes of low-frequency variability related to signals described in the reviewed literature: (1) a secular trend representing the global warming signal with associated superimposed decadal variability; (2) an interdecadal mode with maximal realization in the extratropical North Pacific; and (3) a multidecadal mode with maximal realization in the extratropical North Atlantic. Relationships between SST and precipitation are analyzed with regression and multivariate analyses. These analyses show for the interannual-to-decadal timescales of the Western Hemisphere tropics that tropical Atlantic SST is comparable to the Pacific ENSO in its relevance to regional rainfall and is not redundant with respect to ENSO. Moreover, non-ENSO variability explains a significant fraction of the total cross-covariance between the two variables, and out-of-phase relationships between Pacific and tropical North Atlantic SST anomalies are associated with very strong rainfall departures over Central America and the Caribbean.