Power-law correlations in the southern-oscillation-index fluctuations characterizing El Nino - art. no. 047201

The southern oscillation index (SOI) is a characteristic of the El Nine phe nomenon. SOI monthly averaged data is analyzed far the time interval 1866-2 000. The tail of the cumulative distribution of the fluctuations of SOI sig nal is studied in order to characterize the amplitude scaling of the fluctu ations and the occurrence of extreme events. Large fluctuations are more li kely to occur than the Gaussian distribution would predict. The time scalin g of fluctuations is studied by applying the energy spectrum and the detren ded fluctuation analysis statistical method. Self-affine properties are fou nd to be pertinent to the SOI signal and therefore suggest power-law correl ations of fluctuations of the signal. An antipersistent type of correlation s exists for a time interval ranging from about 4 months to about 6 years. This leads to favoring specific physical models for El Nino description.