The two types of ENSO in CMIP5 models

Seon Tae Kim,Jin‐Yi Yu

doi:10.1029/2012gl052006

Abstract

In this study, we evaluate the intensity of the Central‐Pacific (CP) and Eastern‐Pacific (EP) types of El Niño‐Southern Oscillation (ENSO) simulated in the pre‐industrial, historical, and the Representative Concentration Pathways (RCP) 4.5 experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Compared to the CMIP3 models, the pre‐industrial simulations of the CMIP5 models are found to (1) better simulate the observed spatial patterns of the two types of ENSO and (2) have a significantly smaller inter‐model diversity in ENSO intensities. The decrease in the CMIP5 model discrepancies is particularly obvious in the simulation of the EP ENSO intensity, although it is still more difficult for the models to reproduce the observed EP ENSO intensity than the observed CP ENSO intensity. Ensemble means of the CMIP5 models indicate that the intensity of the CP ENSO increases steadily from the pre‐industrial to the historical and the RCP4.5 simulations, but the intensity of the EP ENSO increases from the pre‐industrial to the historical simulations and then decreases in the RCP4.5 projections. The CP‐to‐EP ENSO intensity ratio, as a result, is almost the same in the pre‐industrial and historical simulations but increases in the RCP4.5 simulation.

Highlights

[1] In this study, we evaluate the intensity of the CentralPacific (CP) and Eastern-Pacific (EP) types of El NiñoSouthern Oscillation (ENSO) simulated in the pre-industrial, historical, and the Representative Concentration Pathways (RCP) 4.5 experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5)
We find that close to 50% of the CMIP5 models still cannot simulate realistically strong EP and CP ENSOs, as was the case for the Coupled Model Intercomparison Project Phase 3 (CMIP3) models
It is more difficult for the models to reproduce the observed EP ENSO intensity than the observed CP ENSO intensity

Summary

Introduction

[2] It has been increasingly recognized that two different flavors or types of El Niño-Southern Oscillation (ENSO) occur in the tropical Pacific [e.g., Wang and Weisberg, 2000; Trenberth and Stepaniak, 2001; Larkin and Harrison, 2005; Yu and Kao, 2007; Ashok et al, 2007; Kao and Yu, 2009; Kug et al, 2009]. Ding et al [2011] related the west Antarctica warming with the three-decade warming trend in the central equatorial Pacific, which was attributed to increasing intensity and frequency of CP El Niño by Lee and McPhaden [2010]. These findings point to a need to examine the different flavors or types of ENSO in the climate models used in the Intergovernmental Panel on Climate Change (IPCC) reports that aim to project future changes in climate variability modes (including ENSO) and their climate impacts. The results obtained in this study indicate that the EP and CP ENSO may not respond in the same way to climate change

Data and Method

Results

Findings

Summary and Discussion