Interaction between equatorially symmetric and asymmetric tropical eastern Pacific SSTs

The third version of the extended reconstructed sea surface temperature (SST) data spanning from 1880 to 2007 was used to investigate the interaction between equatorially symmetric and asymmetric tropical eastern Pacific SSTs. Principal component analysis and wavelet spectrum analysis showed that the asymmetric SST was dominated by an amplitude-modulated annual cycle, while the symmetric SST was a mixture of amplitude-modulated annual cycle and El Niño-Southern Oscillation (ENSO). The symmetric and asymmetric components were significantly correlated, particularly in March and October. In March, when ENSO is usually weak, the interaction between two components is mainly due to the interaction between the amplitude-modulated annual cycles of each component. On the other hand, in October, when ENSO is dominant, the interaction between amplitude-modulated asymmetric annual cycle and ENSO becomes dominant. The interaction in March is partly explained by anomalous southeasterly winds associated with the symmetric SST pattern reducing wind speed over the southeastern Pacific, causing an intensification of the asymmetric SST component. In October, the equatorial asymmetrical development of ENSO causes a significant correlation between the symmetric and asymmetric components.