Effective ENSO Amplitude Forecasts Based on Oceanic and Atmospheric Preconditions

Abstract

Current climate models have relatively high skills in predicting the El Niño-Southern Oscillation (ENSO) phase, i.e., El Niño, neutral and La Niña, once leaping over the spring predictability barrier. However, it is still a big challenge to realistically forecast the ENSO amplitude, for instance, whether a predicted event will be strong, moderate or weak. Here we demonstrate that the accumulated westerly wind events (WWEs)/easterly wind surges (EWSs) and oceanic recharged/discharged states are both of importance in accurate ENSO amplitude forecasts. El Niño and La Niña events exhibit asymmetric temporal and spatial features in the atmospheric and oceanic preconditions. The El Niño amplitude at the peak season is closely associated with the accumulated WWEs over the eastern equatorial Pacific from the previous December to May and the recharged state in the western equatorial Pacific during February. In contrast, the amplitude of La Niña events is sensitive to the accumulated EWSs over the equatorial western Pacific from the previous November to April and the discharged state extending from the equatorial western to central Pacific during February. Considering these asymmetric atmospheric and oceanic preconditions of the El Niño and La Niña cases, a statistical model is established to accurately forecast the ENSO amplitude at its mature phase during 1982-2018, which is validated to be robust based on a one-year cross-validation and independent sample tests. The feasibility and the limitation of the established statistical model are also discussed by examining its practical utility.

Influence of Spring Precipitation over Maritime Continent and Western North Pacific on the Evolution and Prediction of El Niño–Southern Oscillation

“…Many statistical and dynamical models in previous studies have displayed a relatively high skill in predicting ENSO [41,70,71]. However, our primary objective remains to enhance the accuracy of prediction in both the ENSO phase and amplitude.…”

“…Based on the effective atmospheric and oceanic precursors, we have established a robust statistical model for predicting ENSO phase and amplitude. To assess its practical performance, we apply the model for ENSO prediction based on phases predicted by the NCEP Coupled Forecast System version 2 (CFSv2), as in Xuan et al [71]. Specifically, we calculate the Niño-3.4 (D 0 JF 1 ) index for all years predicted as El Niño, neutral or La Niña with a 7-month lead in our statistical forecast model.…”