Evaluating ENSO teleconnections using observations and CMIP5 models

Indrani Roy,Alexandre S Gagnon,Devendraa Siingh

doi:10.1007/s00704-018-2536-z

Abstract

Bias correction of global and regional climate models is essential for credible climate change projections. This study examines the bias of the models of the Coupled Model Inter-comparison Project Phase 5 (CMIP5) in their simulation of the spatial pattern of sea surface temperature (SSTs) in different phases of the El Niño Southern Oscillation (ENSO) and their teleconnections—highlighting the strengths and weaknesses of the models in different oceanic sectors. The comparison between the model outputs and the observations focused on the following three features: (i) the typical horseshoe pattern seen in the Pacific Ocean during ENSO events with anomalies in SSTs opposite to the warm/cool tongue, (ii) different signature in the tropical Pacific Ocean from that of the North and tropical Atlantic Ocean, and (iii) spurious signature in the southern hemisphere beyond 45° S. Using these three cases, it was found that the model simulations poorly matched the observations, indicating that more attention is needed on the tropical/extratropical teleconnections associated with ENSO. More importantly, the observed SST coupling between the tropical Pacific Ocean and the Atlantic Ocean is missing in almost all models, and differentiating the models between high/low top did not improve the results. It also found that SSTs in the tropical Pacific Ocean are relatively well simulated when compared with observation. This work has improved our understanding of the simulation of ENSO and its teleconnections in the CMIP5 models and has raised awareness of the bias existing in the models, which requires further attention by climate modellers.

Highlights

The El Niño Southern Oscillation (ENSO) is the most important tropospheric mode of climate variability, affecting the climate of many parts of the globe through teleconnections
Compositing studies of sea surface temperature (SST) were examined with models based on four chosen criteria: (i) opposite signal outside tropics of Pacific as horseshoe pattern mainly for LNCM and ENCM/ENC, (ii) opposite signature in tropical Pacific and Atlantic for ENM/LNM and ENCM/LNCM, (iii) signal around Greenland for (EN/La Niña (LN)) CM and (EN/LN) M, and (iv) southern hemisphere beyond 45° S—significant change in model SST but not in observation
In all four categories of SST, the models poorly represent the observations, indicating that further work is required on the tropical extra-tropical teleconnections associated with ENSO

Summary

Introduction

The El Niño Southern Oscillation (ENSO) is the most important tropospheric mode of climate variability, affecting the climate of many parts of the globe through teleconnections. Kao and Yu (2009) further examined the structure and evolution of the EP and CP types of ENSO and the teleconnections associated with them Their analysis revealed that the EP type is mainly controlled by a shift in the tropical Pacific thermocline, while for the CP type, atmospheric forcing plays a more important role and it has an extratropical connection. The first theory suggests that anomalous SSTs in the tropical Pacific Ocean are generated by zonal oceanic advection, while the second theory indicates that it is first excited by extratropical forcing in the mid-latitudes and further developed through equatorial oceanic advection Because of their independence in structure, evolution and formation mechanism, this work focuses on different types of ENSO to explore various SST features and related oceanic teleconnection patterns

Methods

Results

Conclusion