Contrasting the termination of moderate and extreme El Niño events in coupled general circulation models
As in the observed record, the termination of El Niño in the coupled IPCC-AR4 climate models involves meridional processes tied to the seasonal cycle. These meridional processes both precondition the termination of El Niño events in general and lead to a peculiar termination of extreme El Niño events (such as those of 1982–83 and 1997–98), in which the eastern equatorial Pacific warm sea surface temperature anomalies (SSTA) persist well into boreal spring/early-summer. The mechanisms controlling the peculiar termination of extreme El Niño events, which involves to the development of an equatorially centred intertropical convergence zone, are consistent across the four models that exhibit extreme El Niños and observational record, suggesting that this peculiar termination represents a general feature of extreme El Niños. Further, due to their unusual termination, extreme El Niños exhibit an apparent eastward propagation of their SSTA, which can strongly influence estimates of the apparent propagation of ENSO over multi-decadal periods. Interpreting these propagation changes as evidence of changes in the underlying dynamical feedbacks behind El Niño could therefore be misleading, given the strong influence of a single extreme event.
KeywordsEl Niño/Southern Oscillation (ENSO) Extreme events IPCC-AR4 climate models Coupled ocean–atmosphere mechanisms Validation
Authors are grateful to Michael McPhaden, Eric Guilyardi, Hilary Weller and an anonymous reviewer for helpful comments. We also acknowledge the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the IPCC Data Archive at Lawrence Livermore National Laboratory (U.S. D.O.E.) for making the IPCC-AR4 model data made available.
- Guilyardi E, Wittenberg A, Fedorov A, Collins M, Wang C, Capotondi A, van Oldenborgh GJ, Stockdale T (2008) Understanding El Niño in Ocean–Atmosphere General Circulation Models : progress and challenges. Bull Am Met Soc (in press)Google Scholar
- Lengaigne M, Boulanger J-P, Menkes C, Madec G, Delecluse P, Guilyardi E, Slingo JM (2003) The March 1997 Westerly wind event and the onset of the 1997/98 El Niño: understanding the atmospheric response. J Clim 16:3330–22243. doi: 10.1175/1520-0442(2003)016<3330:TMWWEA>2.0.CO;2 CrossRefGoogle Scholar
- Meehl G, Covey C, Delworth T, Latif M, McAvaney B, Mitchell J, Stouffer R, Taylor K (2007) The WCRP CMIP3 multimodel dataset: a new era in climate change research. Bull Am Met Soc 1383–1394Google Scholar
- Vecchi GA, Harrison DE (2003) On the termination of the 2002–2003 El Niño event. Geophys Res Lett 30:1964. doi: 10.1029/2003GL017564
- Vecchi GA, Rosati A, Harrison DE (2004) Setting the timing of El Niño termination. Bull Am Met Soc 85:1065–1066Google Scholar
- Wang C, Picaut J (2004) Understanding ENSO physics—A review (2004). In: Wang C, Xie SP, and Carton JA (eds) Earth climate: the ocean–atmosphere interaction. AGU Geosphysical Monograph Series, pp 1–54Google Scholar
- Xiao H, Mechoso CR (2009) Seasonal cycle ENSO Interactions: validation of hypotheses. J Atmos Sci (in press)Google Scholar