Photo Credit: Boris Dewitte, LEGOS, Toulouse, France

The dynamics of El Niño Southern Oscillation (ENSO) rely to a large extent on the forcing of equatorial waves that act on the Sea Surface Temperature through linear and non- linear advection. Recent observed changes in ENSO properties, in particular, the increased occurrence of Central Pacific (or Modoki El Niño) has led to a refinement of the classical view of propagating variability in the tropical Pacific by taking into account the impact of the change in the mean state on the wave caracteristics. Here we review recent progress in the analysis and interpretation of propagating variability in the equatorial Pacific as observed by satellite and simulated by state-of-the-art models. We introduce an extended theory of the existing paradigm of ENSO that is appropriate for estimating the sensitivity of ENSO to climate change.