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.
- Behringer DW, Xue Y (2004) Evaluation of the global ocean data assimilation system at NCEP: The Pacific Ocean. Eighth Symposium on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, and Land Surface, AMS 84th Annual Meeting, Washington State Convention and Trade Center, Seattle, Washington, 11–15Google Scholar
- Braganza K (2008) Seasonal climate summary southern hemisphere (autumn 2007). La Niña emerges as a distinct possibility in 2007. Aust Met Mag 57:65–75Google Scholar
- Conkright ME, Levitus S, O’Brien T, Boyer TP, Stephens C, Johnson D, Baranova O, Antonov J, Gelfeld R, Rochester J, Forgy C (1999) World ocean database 1998 CD-ROM data set documentation, Version 2.0. NODC Internal Report 14, 116ppGoogle Scholar
- Kistler R, Kalnay E, Collins W, Saha S, White G, Woollen J et al (2001) The NCEP–NCAR 50-Year Reanalysis: Monthly means CD-ROM and documentation. Bull Amer Meteor Soc 82:247–267Google Scholar
- Lengaigne M, Vecchi GA (2009) Contrasting the termination of moderate and extreme El Niño events in coupled general circulation models. Climate Dyn. doi: 10.1007/s00382-009-0562-3
- Lukas R (2001) Pacific equatorial currents. In: Steele JH, Thorpe SA, Turekian KA (eds) Encyclopedia of ocean sciences. Academic, LondonGoogle Scholar
- McPhaden MJ, Delcroix T, Hanawa K, Kuroda Y, Meyers G, Picaut J, Swenson M (2001) The El Niño/Southern oscillation (ENSO) observing system. Observing the ocean in the 21st century. In: Koblinsky CJ and Smith NR (Eds) Australian Bureau of Meteorology, p 231–246Google Scholar
- Wang B, Wu R, Lukas R (1999) Roles of the western North Pacific wind variation in thermocline adjustment and ENSO phase transition. J Meteor Soc Japan 77:1–16Google Scholar
- Wang LC, Wu CR (2012) Modulation of the equatorial currents by the two types of El Niño events. Atmosphere–Ocean. doi: 10.1080/07055900.2012.744294
- Wolter K, Timlin MS (1993) Monitoring ENSO in COADS with a seasonal adjusted principal component index. Proc. 17th Climate Diagnostics Workshop. Norman, OK, NOAA/NMC/CAC, 52–57Google Scholar