Understanding the driving mechanisms behind triple-dip La Niñas: insights from the prediction perspective

This study investigates the mechanisms and predictability of multi-year La Niña events, focusing on the 1998–2001 and 2020–2023 triple-dip events, using a physically based statistical ENSO prediction model (EPM). The results highlight distinct driving mechanisms behind these two events. The 1998–2001 event was primarily initiated by substantial negative heat content anomalies in the equatorial Pacific, which resulted from the preceding strong El Niño. These negative heat content anomalies played a crucial role in sustaining cold sea surface temperature anomalies (SSTA) into the third year. In contrast, the 2020–2023 event, which lacked significant negative heat content anomalies, was characterized by persistent equatorial easterly wind anomalies induced by extratropical forcing from the Southern Hemisphere. The EPM successfully captures these differences, with tropical ocean-atmosphere coupling being the dominant factor in predictability for 1998–2001, especially during the second year, whereas extratropical forcing played a key role in improving forecasts for 2020–2023. These findings highlight the importance of incorporating extratropical influences to enhance the prediction skill of multi-year La Niña events, especially those with atypical tropical precursors.