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PMEL Publications Abstract

FY 2025

Improving ENSO prediction at longer lead times: Role of off-equatorial South Pacific heat content

Yang, G., Y. Jin, Y. Zhao, E. Di Lorenzo, M.J. McPhaden, and X. Lin

Geophys. Res. Lett., 52(14), e2024GL114540, doi: 10.1029/2024GL114540, View open access article at AGU/Wiley (external link) (2025)

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.

The off-equatorial South Pacific sea surface height (SP SSH), which represents the ocean heat content, can influence the El Niño-Southern Oscillation (ENSO) development beyond 9 months, thus it may be a signal in ENSO forecast. By using linear dynamical models, we find that SP SSH plays an important role in improving the ENSO predictability, especially at long lead times. We further find that the continuous easterly wind over the central Pacific and the westward warm water accumulation during the previous winter cause the origination of SP SSH anomaly, which finally leads to an El Niño-like pattern.

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