Contrasting the evolution between two types of El Niño in a data assimilation model
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Simulation outputs were used to contrast the distinct evolution patterns between two types of El Niño. The modeled isotherm depth anomalies closely matched satellite sea surface height anomalies. Results for the El Niño Modoki (central Pacific El Niño) corresponded well with previous studies which suggested that thermocline variations in the equatorial Pacific contain an east–west oscillation. The eastern Pacific El Niño experienced an additional north–south seesaw oscillation between approximately 15° N and 15° S. The wind stress curl pattern over the west-central Pacific was responsible for the unusual manifestation of the eastern Pacific El Niño. The reason why the 1982/1983 El Niño was followed by a normal state whereas a La Niña phase developed from the 1997/1998 El Niño is also discussed. In 1997/1998, the Intertropical Convergence Zone (ITCZ) retreated faster and easterly trade winds appeared immediately after the mature El Niño, cooling the sea surface temperature in the equatorial Pacific and generating the La Niña event. The slow retreat of the ITCZ in 1982/1983 terminated the warm event at a much slower rate and ultimately resulted in a normal phase.
KeywordsEastern Pacific El Niño Central Pacific El Niño (El Niño Modoki) Wind stress curl pattern
The authors would like to thank the Editor, Dr. Yukio Masumoto, and the anonymous reviewers for their careful review of the manuscript and detailed suggestions to improve the manuscript. The authors are also grateful to D. J. Shea and colleagues from the NCAR for assistance in processing the GODAS outputs. Authors CRW and LCW were supported by the National Science Council, Taiwan, under grants NSC 100-2119-M-001-029-MY5 and NSC 101-2917-I-003-002.
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