The complex network approach has proved to be a valuable tool for climate and atmospheric sciences in recent years. Here, we show an application of causality ideas in complex networks to infer properties of equatorial wave interactions associated with the Madden–Julian Oscillation (MJO), the dominant component of the atmospheric system on intraseasonal timescales in the equatorial region. We use the normal mode function approach to obtain the time series of baroclinic Kelvin and Rossby mode energies, since both of these wave modes are known to play an important role in the MJO dynamics. The partial directed coherence method reveals the structure of the interaction among those modes and shows that the Kelvin mode is the main driver of the MJO system, transferring energy to the Rossby modes. Investigation on the Kelvin mode information source might help evaluating the state-of-the-art of MJO theories.