The Recharge Oscillator Model of ENSO Revisited: Incorporating the Spatial Structure of Wind Stress Anomalies (Invited Presentation)

The most commonly used conceptual model of ENSO is the Recharge Oscillator (Jin 1997), which describes the evolution of temperature in the eastern equatorial Pacific together with changes in ocean heat content in the west. Over time, this model has been extended to include important nonlinearities, atmospheric noise, and the seasonal cycle. However, while the recharge oscillator describes the key dynamics of ENSO, it does not explicitly treat the spatial structure of zonal wind stress anomalies associated with ENSO. Here, starting with the low frequency approximation of Fedorov (2010), we derive a recharge oscillator model that explicitly incorporates the effect of the spatial structure of wind stress anomalies into the equations. This approach allows us to compute explicitly the frequency and decay/growth rates of ENSO mode as a function of parameters describing the width of wind stress anomalies and their location along the equator. For example, in agreement with GCM studies (Capotondi et al. 2006, Stuivenvolt-Allen 2024), this model shows that the broadening of wind stress anomalies leads to longer ENSO period and greater growth rates. Finally, we discuss the implications of this study for ENSO changes in the warming climate.