Observations based on moored buoy surface measurements have shown that the intraseasonal variability of surface zonal wind associated with the Madden-Julian Oscillation is very effective of inducing oceanic Kelvin waves. The forced intraseasonal Kelvin waves propagate from their excitation region in the western and central Pacific to the eastern Pacific, where they introduce substantial perturbations in the thermocline depth. It is unclear, however, whether such intraseasonal perturbations in the thermocline depth is dominantly linear such that they do not have long-term (e.g., interannual) effect. The intraseasonal characteristics of the wind stress in the equatorial Pacific is examined using ERS1/2 scatterometer products. Five-day mean wind stress time series are used as surface forcing to an oceanic general circulation model. This 'high-frequency forced simulation' is then compared with a 'low-frequency forced simulation' in which wind stress forcing is interpolated from its monthly means so that it contains no intraseasonal signal. The thermocline depths from both simulations are then subject to a monthly mean smoothing. It is shown that the long-term perturbations in the thermocline depth in the eastern Pacific are quite different from the two simulations, indicating a nonlinear effect of the high-frequency forcing. The potential implications of this numerical experiment to ENSO prediction are discussed