The paper by Zebiak and Cane presents a coupled atmosphere-ocean model to study the El Niño/Southern Oscillation (ENSO) phenomenon. The model reproduces key features of observed ENSO, such as the recurrence of warm events at irregular intervals with a preferred period of 3-4 years. The mean sea surface temperature, wind, and ocean current fields are found to determine the spatial structure of ENSO anomalies. The tendency for phase-locking of anomalies is explained by variations in coupling strength associated with the annual cycle in mean fields. Sensitivity studies reveal that the amplitude and time scale of the oscillation are sensitive to parameters affecting atmospheric-ocean coupling strength. Stronger coupling results in larger oscillations with a longer time scale. The variability in equatorial heat content of the upper ocean is a critical element of the model oscillation, increasing before warm events and decreasing sharply during them. The authors present a theory for this variability and the transitions between El Niño and non-El Niño states. They discuss the implications of these results for predicting El Niño events. The model's behavior is analyzed in detail, including the influence of the annual cycle and the role of equatorial heat content in driving the oscillation.The paper by Zebiak and Cane presents a coupled atmosphere-ocean model to study the El Niño/Southern Oscillation (ENSO) phenomenon. The model reproduces key features of observed ENSO, such as the recurrence of warm events at irregular intervals with a preferred period of 3-4 years. The mean sea surface temperature, wind, and ocean current fields are found to determine the spatial structure of ENSO anomalies. The tendency for phase-locking of anomalies is explained by variations in coupling strength associated with the annual cycle in mean fields. Sensitivity studies reveal that the amplitude and time scale of the oscillation are sensitive to parameters affecting atmospheric-ocean coupling strength. Stronger coupling results in larger oscillations with a longer time scale. The variability in equatorial heat content of the upper ocean is a critical element of the model oscillation, increasing before warm events and decreasing sharply during them. The authors present a theory for this variability and the transitions between El Niño and non-El Niño states. They discuss the implications of these results for predicting El Niño events. The model's behavior is analyzed in detail, including the influence of the annual cycle and the role of equatorial heat content in driving the oscillation.