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Simulations of ENSO by CMIP5 Climate Models
Michael, J.-P., Misra, V. and Chassignet, E.P. 2013. The El Niņo and Southern Oscillation in the historical centennial integrations of the new generation of climate models. Regional Environmental Change 13: S121-S130.

The authors write that "validating El Niņo and the Southern Oscillation (ENSO) in coupled ocean-atmosphere climate models is considered to be vital to understand and build confidence in the fidelity of the model (Guilyardi et al., 2009)," partly because "ENSO is one of the best known natural climate variations (Philander, 1990), which is relatively well observed (Zebiak and Cane, 1987; Battisti, 1988; Battisti and Hirst, 1989; Hayes et al., 1991; McPhaden, 1993; Jin, 1997; Neelin et al., 1998) and, in comparison with other natural climate signals, is well understood theoretically (Kirtman, 1997; Clarke, 2008)."

What was done
In the words of Michael et al., they "examined the surface and sub-surface oceanic variables, the coupled feedbacks, and the atmospheric response associated with ENSO variations in centennial integrations forced with the time varying twentieth century emissions of the CMIP5 historical runs."

What was learned
The three U.S. researchers say their analysis shows that (1) "the majority of the CMIP5 models continues to display an erroneous split-ITCZ [intertropical convergence zone] feature," with (2) "a cold SST [sea surface temperature] bias in the equatorial oceans," plus (3) "an overly active ITCZ just south of the equator," and that (4) "the warm bias in the stratiform regions of the eastern subtropical oceans is also prominent," that (5) "there was significant diversity in the CMIP5 historical simulations of the ENSO teleconnection with the southeastern U.S. climate," that (6) "many models produced geopotential height patterns over North America [that are] uncharacteristic of the observed ENSO teleconnection, with either the forced variability being [7] too strong or [8] too weak," that (9) "these erroneous teleconnections were also reflected in the corresponding ENSO-forced rainfall anomalies over the southeastern United States," that (10) "the seasonality of the coupled feedback between the zonal wind stress and SST shows apparent issues with the models," and that (11) there is "only a minority of CMIP5 models whose ENSO power spectrum is comparable to the observed spectrum."

What it means
After literally decades of hundreds of researchers attempting to create a mathematical model capable of reasonably accurately representing the full spectrum of the workings of earth's global climate system, there likely is still a long, long road we have yet to travel before we can even begin to see a satisfactory mathematical construct somewhere in the haze ahead of us.

Battisti, D.S. 1988. The dynamics and thermodynamics of a warming event in a coupled tropical atmosphere/ocean model. Journal of the Atmospheric Sciences 45: 2889-2919.

Battisti, D.S. and Hirst, A.C. 1989. Interannual variability in the tropical atmosphere-ocean system: influences of the basic state, ocean geometry and nonlinearity. Journal of the Atmospheric Sciences 46: 1687-1712.

Clarke, A. 2008. An introduction to the dynamics of El Niņo and the Southern Oscillation. Academic Press, Waltham, Massachusetts, USA, p. 324.

Guilyardi, E., Wittenberg, A., Fedorov, A., Collins, M., Wang, C., Capotondi, A., van Oldenborgh, G.J. and Stockdale, T. 2009. Understanding El Niņo in ocean-atmosphere general circulation models. Bulletin of the American Meteorological Society 90: 325-339.

Hayes, S.P., Mangum, L.J., Picaut, J., Sumi, A. and Takeuchi, K. 1991. TAO: a moored array for real-time measurements in the tropical Pacific Ocean. Bulletin of the American Meteorological Society 72: 339-347.

Jin, F.-F. 1997. An equatorial ocean recharge paradigm for ENSO. Part I: conceptual model. Journal of the Atmospheric Sciences 54: 811-829.

Kirtman, B.P. 1997. Oceanic Rossby wave dynamics and the ENSO period in a coupled model. Journal of Climate 10: 1690-1704.

McPhaden, M.J. 1993. Tradewind fetch related variations in equatorial undercurrent depth, speed, and transport. Journal of Geophysical Research 98: 10.1029/92JC02683.

Neelin, J.D., Battisti, D.S., Hirst, A.C., Jin, F.-F., Wakata, Y., Yamagata, T.S. and Zebiak, E. 1998. ENSO theory. Journal of Geophysical Research 103(C7): 14,261-14,290.

Philander, S.G. 1990. El Niņo, La Niņa, and the Southern Oscillation. International Geophysical Series, Vol. 46. Academic Press, Waltham, Massachusetts, USA, p. 293.

Zebiak, S. and Cane, M.A. 1987. A model for El Niņo Southern Oscillation. Monthly Weather Review 115: 2262-2278.

Reviewed 11 June 2014