Using hindcasts produced by a coupled climate model, this study evaluates whether the model can forecast the observed spatiotemporal complexity in the El Niño−Southern Oscillation (ENSO) during the period 1982−2011: the eastern Pacific (EP), central Pacific‐I (CP‐I) and ‐II (CP‐II) types of El Niño, and the multi‐year evolution events of El Niño occurred in 1986–1988 (i.e., 1986/87/88 El Niño) and La Niña occurred in 1998–2000 (i.e., 1998/99/00 La Niña). With regard to the spatial complexity, it is found that the CP‐I type of El Niño is the easiest to hindcast, the CP‐II is second, and the EP is most difficult to hindcast as its amplitude is significantly underestimated in the model used here. The model deficiency in hindcasting the EP El Niño is related to a warm bias in climatological sea surface temperatures (SSTs) in the tropical eastern Pacific. This warm bias is related to model biases in the strengths of the Pacific Walker circulation and South Pacific high, both of which are notably weaker than observed. As for the temporal complexity, the model successfully hindcasts the multi‐year evolution of the 1998/99/00 La Niña but fails to accurately hindcast the 1986/87/88 El Niño. This contrasting model performance in hindcastingmore »
The observed El Niño and La Niña exhibit different complexities in their event‐to‐event transition patterns. The El Niño is dominated in order by episodic, cyclic, and multiyear transitions, but the reversed order is found in the La Niña. A subtropical Pacific onset mechanism is used to explain this difference. This mechanism triggers El Niño/La Niña events via subtropical processes and is responsible for producing multiyear and episodic transitions. Its nonlinear responses to the tropical Pacific mean state result in more multiyear transitions for La Niña than El Niño and more episodic transitions for El Niño than La Niña. The CMIP5/6 models realistically simulate the observed transition complexity of El Niño but fail to simulate the transition complexity of La Niña. This deficiency in CMIP5 models arises from a weaker than observed subtropical onset mechanism and a cold bias in the tropical Pacific mean sea surface temperatures in the models.
- Award ID(s):
- 1833075
- Publication Date:
- NSF-PAR ID:
- 10448360
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 16
- ISSN:
- 0094-8276
- Publisher:
- DOI PREFIX: 10.1029
- Sponsoring Org:
- National Science Foundation
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