The Principal Physical Modes of Variability over the Tropical Pacific

Abstract

The structures of the two principal modes of sea surface temperature (SST) variability were extracted by conducting cyclostationary EOF (CSEOF) analysis and regression analysis on several key variables. The CSEOF analysis extracts two dominant modes of SST variability that are distinct in nature. The first CSEOF is stochastic in nature and represents a standing mode of SST variability associated with a basinwide change in the surface wind. The second CSEOF exhibits a strong deterministic component describing a biennial oscillation between a warm phase and a cold phase. The surface wind directional change in the far-western Pacific appears to be instrumental for the oscillation between the two phases. Because of the distinct nature of evolution, dynamical and thermodynamical responses of the two modes are different. Further, the predictability of the two modes is different. Specifically, the biennial mode is more predictable because of the strong deterministic component associated with its evolution. The distinction of the two modes, therefore, may be important for predicting ENSO. The irregular interplay of the two modes seems to explain some inter-ENSO variability, namely, variable duration of ENSO events, approximate phase-locking property, and irregular onset and termination times.