a Institute of Physics, Humboldt University, Invalidenstrasse 110, 10115 Berlin, Germany
b Leibniz Sozietät, P.O. Box 840126, 12531 Berlin, Germany
Abstract:
Entropy analysis and wavelet transforms are used to study the Southern Oscillation index (SOI) and multivariate ENSO index (MEI) indexes for the El Niño–Southern Oscillation. Trends to large decreasing symbolic chains responsible for La Niña and interrupted increasing chains for El Niño are found in the MEI persistence series. These are all located in regions where the wavelet transforms of both indexes reveal the existence of mid-range correlations. The SOI and MEI indexes are mutually correlated in a non-trivial manner in the time.