Analysis of the Relationship between ENSO Amplitude and the Internal Variability

Abstract:

ENSO is the most predominant interannual climate variability in Earth and how the ENSO properties would be changed under global warming is a central issue in climate community. In particular, it is necessary to understand how the internal variability, which rises from atmospheric, oceanic, land, and cryospheric processes and their coupled interactions, contributes to the uncertainties of ENSO in a changing climate. By using CESM large ensemble runs, we analyze the relationship of ENSO amplitude and internal variability under global warming. The CESM large ensemble contains 30 members using the same model and the same external forcing from the historical run to the RCP8.5 run. It is found that the change in the ENSO amplitude due to internal variability is large, in addition, such a contribution of internal variability is not much changed under global warming. We further found that a possible reason why the ENSO amplitude changes under global warming is so diverse among climate models might be associated with the amplitude in the internal variability in the historical period.