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Professor Jin-Yi Yu
Department of Earth System Science
University of California, Irvine

ENSO Simulation, Dynamics, and Prediction

View the simulated ENSO cycle here.


The performance of the UCLA coupled GCM (CGCM) has been greatly improved in recent years. The model produces ENSO-type variability with large amplitudes. The simulated cycle is characterized by predominantly standing oscillations of SST in the eastern Pacific, almost simultaneous zonal wind stress anomalies to the west of the SST anomalies, and preceding thermocline anomalies near the western edge of the basin. The above figure shows the three-dimensional evolution of ocean temperature anomalies in the tropical Pacific during the ENSO cycle. The evolution is characterized by four major movements: (1) the build up of temperature anomalies in the subsurface of the western equatorial Pacific during the pre-onset phase of ENSO; (2) the fast spread of the anomalies from the western subsurface to the eastern surface of the equatorial Pacific during the onset phase, (3) the zonal extension and amplification of surface anomalies during the growth phase, and (4) the northward and downward spread of temperature anomalies during the decay phase.


The fundamental physical processes that give rise to El Nino-Southern Oscillation (ENSO) are believed to be within the tropical Pacific. We use the simulated ENSO cycle obtained by Yu and Mechoso (2001) from a 53-year long CGCM simulation to examine two conceptual models of ENSO: the recharge-oscillator and the delayed-oscillator model. During the simulated ENSO cycle, ocean heat content anomalies in the tropical Pacific are characterized by a meridional oscillation between the equator and 10N and a zonal oscillation between the western and eastern equatorial Pacific. The meridional mode appears to be related to the phase-transition of the cycle, and the zonal mode is related to the growth of the cycle. We also perform ocean temperature budget analysis to determine the relative importance of various ocean processes in producing subsurface ocean memory for the ENSO cycle. Our analyses indicate that the simulated ENSO cycle is consistent with several major features described by two leading simple models of ENSO: the recharge-oscillator and the delayed-oscillator.


Encouraging results are produced from the experimental long-range prediction made with the UCLA CGCM for the '97-'98 ENSO event. The SST anomalies predicted by the forecast initialized in June 1997 showed that the '97-'98 ENSO had a rapid growth from the June initial condition to the September-October maximum. The model also predicted that, after October 1997, this ENSO event would enter a slowly decaying phase and will be terminated after the spring of 1998. This experimental prediction shows that the '97-'98 ENSO is characterized by a rapid growing phase followed a slow decay. Its forecast of the NINO3 SST anomalies appears to be close to those forecasts made with several models that have been routinely used for long-range prediction. It is shown that the UCLA CGCM has the potential of making long-term prediction with reasonable success.

Related Publications

  • Yu, J.-Y., 2005: Understanding El Nino Southern Oscillation and its interactions with the Indian Ocean and monsoon. Book chapter in Recent Progress in Atmospheric Sciences with Applications to the Asia-Pacific Region, submitted
  • Yu, J.-Y. , 2005: Enhancement of ENSO's persistence barrier by biennial variability in a coupled atmosphere-ocean general circulation model. Geophysical Research Letters, 32, L13707, doi:10.1029/2005GL023406.
  • Yu, J.-Y., C. R. Mechoso, J. C. McWilliams, and A. Arakawa 2002: Impacts of the Indian Ocean on the ENSO cycle. Geophysical Research Letters, 29(8), 1204, doi:10.1029/2001GL014098.
  • Yu, J.-Y. and C.R. Mechoso, 2001: A coupled atmosphere-ocean GCM study of the ENSO cycle. Journal of Climate, 14, 2329-2350.
  • Yu, J.-Y., W. T. Liu, and C.R. Mechoso, 2000: The SST anomaly dipole in the Northern Subtropical Pacific and its relationship with ENSO. Geophysical Research Letters, 27, 1931-1934.
  • Mechoso, C. R., J.-Y. Yu, and A. Arakawa, 2000: A coupled GCM pilgrimage: From climate catastrophe to ENSO simulations. Book Chapter in General Circulation Model Development: Past, Present, and Future., D. A. Randall, Eds., Academic Press, 807pp.
  • Mechoso, C. R., J. D. Farrara, L.A. Drummond, J. Spahr and J.-Y. Yu, 2000: An atmosphere-ocean model: Code optimization and application to El Nino. Book Chapter in Development and Application of Computer Techniques to Environmental Studies VIII., D. A. Gabriel Ibarra-Berastegi, C. A. Brebbia and P. Zanetti, Eds, WIT Press, Southampton, Boston, 261-278.
  • Yu, J.-Y., and C.R. Mechoso, 1999 : Links between annual variations of Peruvian stratocumulus clouds and of SSTs in the eastern equatorial Pacific. Journal of Climate, 12, 3305-3318.
  • Yu, J.-Y., C. R. Mechoso, and C.-C. Ma, 1999: El Nino simulation and prediction using coupled atmosphere-ocean general circulation model. Proceedings of the 1999 International Conference on Mission Earth, 17-20 January 1999, San Francisco, California, 43-48.

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