Nonlinear and linear 412-layer ocean models are used to explore the dynamics of intraseasonal (20--90 day periods) zonal flow in the equatorial Indian Ocean. The model simulations suggest that the observed 40--60 day zonal surface current is forced primarily by wind associated with the Madden-Julian Oscillation (MJO), which peaks at 40--60 days. The strongest spectral peak of zonal flow, however, occurs at 90-day period in the model and a corresponding 90-day peak appears in the observed sea level data. The 90-day current results from the preferential excitation of Kelvin and Rossby waves by the lower-frequency component of intraseasonal wind and from the enhancement by Rossby waves reflected from the eastern ocean boundary. ¿ 2001 American Geophysical Union