Evaluation of El Niño-Southern Oscillation in the ACCESS coupled model simulations for CMIP5

Abstract

One of the key performance measures for Coupled General Circulation Models (CGCMs) is their ability to realistically simulate the prominent modes of climate variability. Here, we investigate the realism of El Niño-Southern Oscillation (ENSO), the dominant mode of observed interannual climate variability, as simulated by the Australian Community Climate and Earth System Simulator (AC-CESS). We examine the key ENSO properties calculated from observations and from the pre-industrial control and historical simulations performed by versions 1.0 and 1.3 of the ACCESS coupled model (ACCESS-CM), as part of the Coupled Model Intercomparison Project phase 5 (CMIP5). The ENSO properties examined are the spatial structure and timescales, phase locking to the annual cycle, growth and decay of Niño3 SST anomalies, and the coupled ENSO evolution, as well as the ENSO induced teleconnection patterns (as diagnosed by linear regressions of the three-dimensional atmospheric circulation field, rainfall, sea-level pressure, and the upper-tropospheric geopotential heights onto the Niño3 index). The coupled evolutions of SST, zonal wind stress, and the thermocline depth during a typical ENSO event are used to illustrate the essential features of ENSO dynamics. Our results show that both versions of the ACCESS-CM perform reasonably well in simulating the ENSO properties and teleconnections. In particular, the spatial structure, timescales, phase locking, and the growth and decay rates of ENSO are well simulated. The evolution of SST, zonal wind stress, and the thermocline depth during ENSO events is also reasonably well simulated, although the SST (zonal wind stress) response is found to be stronger (weaker) than observed. The simulated ENSO teleconnection patterns are also mostly realistic, despite some adverse impact of the equatorial Pacific cold SST bias on the local precipitation response. The present study shows that the ACCESS-CMs simulate the key ENSO properties (e.g. amplitude and spatial structure, timescales, and atmospheric teleconnections) better than most of the previous generations of CGCMs.

The relative performance of Australian CMIP5 models based on rainfall and ENSO metrics

“…The ACCESS.1.0 model also captures the seasonal cycle relatively well (r = +0.75) whereas the ACCESS1.3 model performs relatively poorly (r = 0.23), a finding also reported by Rashid et al (2013). These differences are consistent with the findings of who found that CMIP5 models exhibited a clear improvement over CMIP3 models in simulating key ENSO features.…”

“…These differences are consistent with the findings of who found that CMIP5 models exhibited a clear improvement over CMIP3 models in simulating key ENSO features. Rashid et al (2013) also note that the ACCESS models simulate key ENSO better than most of the previous generation models.…”

“…For example, Watterson et al (2013) describes the assessment of models using metrics related to the spatial features, the variability and teleconnection patterns for several variables. Perkins et al (2012) and Rashid et al (2013) use metrics based on ENSO-related features such as frequency, the spatial SST anomaly patterns and links between ENSO and other climate variables. Here we focus on metrics which provide some insight into how well the models simulate key features of Australian rainfall and ENSO as revealed in Figs 2 and 3.…”

“…The atmospheric component for ACCESS1.0 is based on the Met Office Hadley Centre model HadGEM2 (version r1.1) while the component for ACCESS1.3 is based on the Met Office's subsequent Global Atmosphere (GA) 1.0. For further details see Bi et al (2013), Dix et al (2013), Rashid et al (2013), and Watterson et al (2013).…”

A skill score based evaluation of simulated Australian climate

“…This assessment regarding equatorial SSTs is specific to PID, as Rashid et al (2013) found that ACCESS1.0 performed at least as well as ACCESS1.3 in simulating the ENSO cycle in the eastern Pacific, although with somewhat smaller amplitude than observed.…”