Time-frequency variability of ENSO and stochastic simulations

Abstract

The time-frequency spectral structure of El Nino-Southern Oscillation (ENSO) time series holds much information about the physical dynamics of the ENSO system. The authors have analyzed changes of the spectrum with time of three ENSO indices: the conventional Southern Oscillation index (SOI), Nino3 sea surface temperatures, and a tropical Pacific rain index, over the period 1871-1995. Three methods of time-frequency analysis-windowed Fourier transform, wavelet analysis, and windowed Prony's method-were used, and the results are in good agreement. The time-frequency spectra of all the series show strong multidecadal variations over the past century. In particular, there was reduced activity o..