The Effect of Equatorial HighFrequency Zonal WindForcing on ENSO Amplitude

What controls ENSO amplitude remains controversial. The authors explore the effect of a kind of idealized equatorial highfrequency zonal wind forcing on ENSO amplitude. This problem is first transformed into a nonlinear optimization problem related to model parameters. Based on a theoretical ENSO model, the role of highfrequency zonal wind forcing in modulating ENSO amplitude is explored. The results show that there are two kinds of highfrequency zonal wind forcings for ENSO events, where the differences lie in the amplitude of the forcing, the period, and the phase. These differences make one kind of forcing enhance the El Nino event, but suppress the La Nina event,while the other kind suppresses the El Nino event and enhances the La Nina event. The further analysis shows that the phase of the highfrequency zonal wind forcing determines the forcing whether enhances ENSO events or suppresses them, while the amplitude and period of the forcing control the degree of its effect on ENSO intensity. Both of these two types of forcings affect ENSO amplitude mainly by the adjustment of oceanic wave on the thermocline.