My last comment:
> "The supposedly simplest "toy" models of ENSO that we describe on the Azimuth Project wiki page here http://www.azimuthproject.org/azimuth/show/ENSO are the ones that remarkably work the best to describe the actual dynamics. If the delayed action oscillator (minus the cubic term) is combined with a seasonally-modulated lunar forcing that's essentially all that is needed to train the model."

Elaborated further here:
http://contextearth.com/2017/06/23/ensoqbo-elevator-pitch/