DEFINITION OF EL NINO AND LA NINA EVENTS

M. A. Petrosyants and D. Yu. Gushchina

The structure of sea surface temperature anomalies (SSTA) in the Nino 3 region in the equatorial Pacific is studied in detail for justification of their use as a criterion of El Nino and La Nina detection in a continuous SSTA series for 1948–1997. It is shown that the most realistic threshold SSTA value for El Nino detection in the Nino 3 region is SSTA ≥ 0.5°C and for La Nina it is SSTA ≤ 0.5°C. The proposed method of detection of these phenomena made it possible to detect 13 El Nino and 18 La Nina events in the SSTA series in the Nino 3 region from 1948 to 1997. It is shown that the distribution of SST anomalies in the study region does not correspond to normal distribution. Therefore, the empirical probability of La Nina occurrence is 1.7 times greater than that for El Nino, although it could be only a property of the sample used in this study. Relationships are found between both events and global atmospheric circulation features.