ENSO Warm (El Niño) and Cold (La Niña) Event Life Cycles: Ocean Surface Anomaly Patterns, Their Symmetries, Asymmetries, and Implications

Abstract

Previous studies by the authors have described the composite global marine surface anomalies of ENSO warm (El Niño) events and cold (La Niña) events. Here the similarities and differences in these life cycles are examined. Qualitatively different behavior between warm events and cold events exists in the tropical Indian and Atlantic Oceans and in the extratropical Pacific. Even in the tropical Pacific statistically significantly different behavior is found in some variables for particular regions and phases of the life cycles. A single-mode regression analysis of the ENSO signal is done; the patterns are very similar to those of previously published ENSO EOF and regression analyses. The authors describe how the regression patterns obscure many of the interesting life cycles and life cycle differences of cold events and warm events. Most of the regression structures outside of the tropical Pacific are not statistically significant because of such differences. ENSO models should be evaluated against their ability to reproduce the observed cold event and warm event life cycles and not just single EOF or regression mode patterns.