Improving ENSO Prediction at Longer Lead Times: Role of Off‐Equatorial South Pacific Heat Content Geophysical Research Letters

Previous studies have demonstrated that signals originating from the South Pacific can improve the El Niño‐Southern Oscillation (ENSO) prediction at various lead times. In this study, it is found that sea surface height anomalies in the off‐equatorial South Pacific (SP SSH), potentially improves ENSO prediction with lead times exceeding 9 months. Using linear inverse models, we find that SP SSH anomalies and the associated accumulation of warm water result from continuous easterly winds over the tropical central Pacific that force downwelling Rossby waves in the off‐equatorial South Pacific. These downwelling Rossby waves reflect into equatorial downwelling Kelvin waves that propagate into the central and eastern Pacific, ultimately leading to an El Niño event in the following winter.