The seasonal relationship between intraseasonal tropical variability and ENSO in CMIP5

Tatiana Matveeva,Boris Dewitte,Daria Gushchina

doi:10.5194/gmd-11-2373-2018

Abstract

Abstract. The El Niño–Southern Oscillation (ENSO) is tightly linked to the intraseasonal tropical variability (ITV) that contributes to energise the deterministic ocean dynamics during the development of El Niño. Here, the relationship between ITV and ENSO is assessed based on models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) taking into account the so-called diversity of ENSO, that is, the existence of two types of events (central Pacific versus eastern Pacific El Niño). As a first step, the models' skill in simulating ENSO diversity is assessed. The characteristics of the ITV are then documented revealing a large dispersion within an ensemble of 16 models. A total of 11 models exhibit some skill in simulating the key aspects of the ITV for ENSO: the total variance along the Equator, the seasonal cycle and the characteristics of the propagation along the Equator of the Madden–Julian oscillation (MJO) and the convectively coupled equatorial Rossby (ER) waves. Five models that account realistically for both the two types of El Niño events and ITV characteristics are used for the further analysis of seasonal ITV ∕ ENSO relationship. The results indicate a large dispersion among the models and an overall limited skill in accounting for the observed seasonal ITV ∕ ENSO relationship. Implications of our results are discussed in light of recent studies on the forcing mechanism of ENSO diversity.

Highlights

The El Niño–Southern Oscillation (ENSO) is the dominant mode of climate variability at interannual timescale in the Pacific (Bjerknes, 1969; Rasmusson and Carpenter, 1982)
We question the extent to which the models that are used for assessing the change in ENSO properties under global warming (i.e. CMIP phase 5 (CMIP5)) are able to account for a fundamental ENSO property found in the observations, that is, the tendency of intraseasonal tropical variability (ITV) activity to increase one to two seasons prior to the ENSO peak (McPhaden et al, 2006; Hendon et al, 2007; Gushchina and Dewitte, 2012)
A large dispersion among these five models is found in terms of the lag correlation between ITV and the two ENSO indices accounting for both types of events (Figs. 10 and 11)

Summary

Introduction

The El Niño–Southern Oscillation (ENSO) is the dominant mode of climate variability at interannual timescale in the Pacific (Bjerknes, 1969; Rasmusson and Carpenter, 1982). It originates in the equatorial Pacific and induces important climate and weather anomalies in many parts of the globe through so-called teleconnections (Horel and Wallace, 1981; Keshavamurti , 1982; Trenberth et al, 1998; Diaz et al, 2001). Limitations in our ability to forecast El Niño are largely associated with difficulty in realistically simulating the ITV (Lin et al, 2006) that acts as a stochastic atmospheric trigger with regards to the deterministic recharge–discharge process (Jin, 1997)

Objectives

Methods

Results

Conclusion