Defining El Niño indices in a warming climate

Abstract Extreme weather and climate events associated with El Niño La Niña cause massive societal impacts. Therefore, observations forecasts are used around the world to prepare for such events. However, global warming has caused warm seem bigger than they are, while cold smaller, in commonly Niño3.4 index (sea surface temperature (SST) anomalies over 5 ∘ S–5 N, 120–170 W). We propose a simple elegant adjustment, defining relative as difference between original SST anomaly all tropical oceans (20 S–20 N). This describes onset of convection better, is not contaminated by can be monitored forecast real-time. show that better line effects on rainfall would more useful preparedness changing Niño—Southern Oscillation research.