Abstract

The El Niño-Southern oscillation (ENSO) is shown to have undergone significant changes in variance and coherency over the last 130 years. Wavelet analysis is applied to sea surface temperature anomalies (Niño3 SSTA) index to obtain frequencies of the temporal variations in the signal. This technique works in terms of specific events while allowing a researcher to keep an eye on the ensemble properties. By using this relatively new method, our study aims at investigating a quantitative measure of changes in ENSO variance on long-term time scales. Using ERSST.v3b SSTA averaged over the Niño3 region (5 N-5 S 150-90 W) that extend back to 1880, the wavelet analysis show significantly higher events during 1885 to 1920 and 1960 to 2005, and lower events during 1920 to 1960. Most of the power is concentrated within the ENSO band of 2 to 8 years.

Key words: Morlet wavelet, Niño3 region, sea surface temperature anomalies, variability, wavelet power spectra.