Recent progress on two types of El Nio: Observations, dynamics, and future changes

The climate community has made significant progress in observing, understanding and predicting El Nio and Southern Oscillation (ENSO) over the last 30 years. In spite of that, unresolved questions still remain, including ENSO diversity and extreme events, decadal modulation, predictability, teleconnection, and the interaction of ENSO with other climate phenomena. In particular, the existence of a different type of El Nio from the conventional El Nio has been proposed. This type of El Nio has occurred more frequently during the recent decades and received a great attention in the climate community. This review provides recent progresses on dynamics, decadal variability and future projection of El Nio, with a focus on the two types of El Nino.