Predictability of the Decay of the 1982/83 El Niño

Abstract

A dynamical forecast model which has been applied to the onset of the 1982/83 El Niño is applied to the decay of this event. The timing of the decay is well predicted, illustrating the flexibility of the dynamical forecast model which could handle an unusual El Niño, i.e., the 1982/83 event with significant wind changes outside a well-recognized site for usual El Niño related wind changes. The results suggest the need to include zonal winds from the entire equatorial Pacific. It appears that the dynamical forecast model based on a linear numerical model forced by ship winds can be used to forecast the timing of the onset and decay of a major El Niño. The evolution of the 1982/83 El Niño is described using the dynamical model forced by the observed wind. The equatorial Pacific Ocean response during this event is basically that to an eastward translating zonal band of westerly wind anomalies. The observed double peaks in the sea-level record in the eastern Pacific in early 1983 appear to be due to the observed amplitude modulation of the wind anomalies east of 140°W, confirming the previous findings of Tang and Weisberg. It appears that the first Kelvin wave pulse generated in the western Pacific in early 1982 was reflected as a Rossby wave from the eastern boundary. The propagation of this Rossby wave into the central Pacific in July 1982 coincides with the dramatic intensification of the westerly wind anomalies in that region. This suggest a possible air-sea interaction leading to the major onset of this El Niño.