The S-transform for obtaining localized spectra

Abstract

We used the recently developed S-transform, an extension to the ideas of Gabor transform and wavelet transform, to analyze the Tropical Ocean Global Atmosphere (TOGA) sea level data set and to obtain the localized spectra, varying with time. Our S-spectra show some features that cannot be obtained from the Fourier transform, such as a phase lock, temporal variability of spectra, and out of phase-behavior of the semiannual, annual, and biannual signals between the western Pacific (Naura) station and the eastern Pacific (La Libertad) station. The annual signal is usually phase locked with the semiannual, but not with the biannual signal. The annual signal is quite stationary in the western Pacific station and non-stationary in the eastern Pacific station. During 1980-84, the quasi-biannual (QB) signal was very strong at the western Pacific station and quite weak at the eastern Pacific station. However, during 1974-76 and 1986-90, the QB signal was weak at the western Pacific station and strong at the eastern Pacific station. This may imply different physical processes involved in the western and eastern Pacific during the El Nino and Southern Oscillation (ENSO) periods.