What Controls ENSO‐Amplitude Diversity in Climate Models?

Climate models depict large diversity in the strength of the El Niño/Southern Oscillation (ENSO) (ENSO amplitude). Here we investigate ENSO‐amplitude diversity in the Coupled Model Intercomparison Project Phase 5 (CMIP5) by means of the linear recharge oscillator model, which reduces ENSO dynamics to a two‐dimensional problem in terms of eastern equatorial Pacific sea surface temperature anomalies ( T ) and equatorial Pacific upper ocean heat content anomalies ( h ). We find that a large contribution to ENSO‐amplitude diversity originates from stochastic forcing. Further, significant interactions exist between the stochastic forcing and the growth rates of T and h with competing effects on ENSO amplitude. The joint consideration of stochastic forcing and growth rates explains more than 80% of the ENSO‐amplitude variance within CMIP5. Our results can readily explain the lack of correlation between the Bjerknes Stability index, a measure of the growth rate of T , and ENSO amplitude in a multimodel ensemble.