We thank Ping Chang for most useful comments, Larry Rosen for his help in running the model, and Ilya Rivin for useful discussions. This work is partially supported by a grant from NOAA through the Consortium for Climate Research, UCSIOPO-10775411D/ NA47GP0188. Two of the authors (SZ and MC) are also partially supported by NSF Grant ATM92-24915.
Battisti, D. S., 1988: The dynamics and thermodynamics of a warming event in a coupled tropical atmosphere–ocean model. J. Atmos. Sci.,45, 2889–2919.
——, and A. C. Hirst, 1989: Interannual variability in the tropical atmosphere–ocean system: Influence of the basic state, ocean geometry and nonlinearity. J. Atmos. Sci.,46, 1687–1712.
——, and E.S. Sarachik, 1995: Understanding and predicting ENSO. Rev. Geophys.33 (Suppl.), 1367–1376.
Blumenthal, M. B., 1991: Predictability of a coupled ocean-atmosphere model. J. Climate,4, 766–784.
Cane, M. A., M. Munnich, and S. E. Zebiak, 1990: A study of self-excited oscillations of the tropical ocean–atmosphere system. Part I: Linear analysis. J. Atmos. Sci.,47, 1562–1577.
Chang, P., 1994: A study of the seasonal cycle of sea surface temperature in the tropical Pacific Ocean using reduced gravity models. J. Geophys. Res.,99, 7725–7741.
——, B. Wang, T. Li, and L. Ji, 1994: Interactions between the seasonal cycle and the southern oscillation—Frequency entrainment and chaos in a coupled ocean–atmosphere model. Geophys. Res. Lett.21, 2817–2820.
——, L. Ji, B. Wang, and T. Li, 1995: Interactions between the seasonal cycle and El Niño–Southern Oscillation in an intermediate coupled ocean–atmosphere model. J. Atmos. Sci.,52, 2353–2372.
Chen, D., S. E. Zebiak, A. J. Busalacchi, and M. A. Cane, 1995: An improved procedure for El Niño forecasting: Implications for predictability. Science,269, 1699–1702.
Goswami, B. N., and J. Shukla, 1991: Predictability of a coupled ocean–atmosphere model. J. Climate,4, 107–115.
Graham, N. E., and W. B. White, 1988: The El Niño cycle: A natural oscillator of the Pacific ocean–atmosphere system. Science,240, 1293–1302.
Hirst, A. C., 1986: Unstable and damped equatorial modes in simple coupled ocean–atmosphere models. J. Atmos. Sci.,43, 606–630.
Jin, F.-F., D. Neelin, and M. Ghil, 1994: ENSO on the devil’s staircase. Science,264, 70–72.
Koberle, C., and S. G. H. Philander, 1994: On the processes that control seasonal variations of sea surface temperatures in the tropical Pacific Ocean. Tellus,46A, 481–496.
Latif, M., T. P. Barnett, M. A. Cane, M. Flugel, N. E. Graham, H. von Storch, J.-S. Xu, and S. E Zebiak, 1994: A review of ENSO prediction studies. Climate Dyn.,9, 167–179.
Mantura, N. J., and D. S. Battisti, 1995: Aperiodic variability in the Zebiak–Cane coupled ocean–atmosphere model: Air–sea interactions in the western equatorial Pacific. J. Climate,8, 2897–2927.
Munnich, M., M. A. Cane, and S. E. Zebiak, 1991: A study of self-excited oscillations of the tropical ocean–atmosphere system. Part II: Nonlinear cases. J. Atmos. Sci.,48, 1238–1248.
Neelin, J. D., 1991: The slow sea surface temperature mode and the fast-wave limit: Analytic theory for tropical interannual oscillations and experiments in a hybrid coupled model. J. Atmos. Sci.,48, 584–606.
Philander, S. G., 1983: El Niño–Southern Oscillation phenomena. Nature,302, 295–301.
——, 1990: El Niño, La Niña, and the Southern Oscillations. Academic Press, 293 pp.
——, T. Yamagata, and R. C. Pacanowski, 1984: Unstable air–sea interactions in the tropics. J. Atmos. Sci.,41, 604–613.
Rasmusson, E., and T. Carpenter, 1982: Variations in the tropical sea surface temperature and surface wind fields associated with the Southern Oscillation/El Niño. Mon. Wea. Rev.,110, 354–384.
Suarez, M. J., and P. S. Schopf, 1988: A delayed action oscillator for ENSO. J. Atmos. Sci.,45, 3283–3287.
Tziperman, E., L. Stone, M. Cane, and H. Jarosh, 1994: El Niño chaos: Overlapping of resonances between the seasonal cycle and the Pacific ocean–atmosphere oscillator. Science,264, 72–74.
——, M. A. Cane, and S. Zebiak, 1995: Irregularity and locking to the seasonal cycle in an ENSO prediction model as explained by the quasi-periodicity route to chaos. J. Atmos. Sci.,52, 293–306.
Xue, Y., M. A. Cane, S. E. Zebiak, and M. B. Blumenthal, 1994: On the prediction of ENSO: A study with a low-order Markov model. Tellus,46A, 512–528.
Zebiak, S. E., 1986: Atmospheric convergence feedback in a simple atmospheric model for El Niño. Mon. Wea. Rev.,114, 1263–1271.
——, and M. Cane, 1987: A model El Niño–Southern Oscillation. Mon. Wea. Rev.,115, 2262.