ENSO Transition Complexity and Its Underlying Dynamics in CMIP6 Models

Transitions from one El Niño-Southern Oscillation (ENSO) event to another can occur in various ways and constitute a key element of ENSO complexity. While ENSO amplitude, periodicity, and flavor in CMIP models have been frequently examined, ENSO transition complexity in models has not been as thoroughly evaluated. We developed a dynamic framework to explain how three transition patterns (i.e., episodic ENSO, cyclic ENSO, and multi-year ENSO) are produced and use this framework to examine CMIP6 model simulations and projections. The dynamic framework focuses on the ENSO onset dynamics, rather than the ENSO growth dynamics that are more often discussed for other ENSO properties. In this talk, we will discuss (1) how well the ENSO transition complexity and its underlying dynamics are simulated in CMIP5 and CMIP6 models; and (2) how the complexity dynamics affect the model projections of future ENSO complexity. We will also further discuss the ENSO complexity metrics we developed for the evaluations.