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Kumar, A., and M. P. Hoerling, 1997: Interpretation and implications of observed inter-El Niño variability. J. Climate, 10, 83-91.


ABSTRACT

The variability in extratropical atmospheric anomalies from one El Niño winter to another is examined. This study offers an interpretation for such observed inter-El Niño variations and discusses implications for seasonal atmospheric predictability.

The seven strongest El Niño events of the 1950-94 period are selected in order to form a composite 500-mb circulation anomaly over the Pacific-North American region. Individual events are shown to deviate significantly from such a composite. Using a large ensemble of atmospheric general circulation model simulations forced with the observed sea surface temperatures of 1950-94, the authors argue that the observed inter-El Niño atmospheric variations are primarily due to internal atmospheric variability. The observed inter-El Niño variability in spatial patterns of the extratropical circulation anomalies appears not to be a deterministic feature of the SSTs and may thus be inherently unpredictable.

Atmospheric general circulation model results further suggest that the spatial pattern of the extratropical response to El Niño consists largely of a single deterministic structure. Some variability in the spatial pattern of the simulated extratropical signal exists, but this is appreciably smaller than the internal atmospheric variability. On the other hand, the amplitude of the signal in the extratropics is shown to be a sensitive function of the particular El Niño, and the model response increases almost linearly with the strength of the SST warming. The practical implications for dynamic seasonal climate prediction in the extratropics are discussed, including an assessment of accuracy requirements for the SST predictions themselves.