Parallel Session 3: Harun Rashid: An analysis of ENSO simulation biases in ACCESS-CM2 for CMIP6

ACCESS Workshop 2025 ACCESS Workshop Day 2
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An analysis of ENSO simulation biases in ACCESS-CM2 for CMIP6

Harun Rashid


1. Introduction
Global climate models show systematic errors in simulating El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability. This is despite a substantial improvement in ENSO simulations by climate models over recent years. The simulated ENSO in ACCESS-CM2 has a period around 2.5 years, shorter than the observed periods of 3-7 years. Here, we investigate this ACCESS-CM2 bias, with the expectation that understanding this bias will improve ENSO simulation in subsequent versions of ACCESS.

  1. Methodology
    We use ACCESS-CM2 outputs from the CMIP6 archive and a set of 20 perturbed physics experiments and analyse these data with a statistical model based on the recharge-discharge oscillator model of ENSO.

  2. Results
    Our analysis shows that ENSO periods in ACCESS-CM2 simulations are predominantly controlled by the strength of the thermocline feedback. A stronger thermocline feedback favours a shorter ENSO time scale and vice-versa. Consistent with having a shorter ENSO period, ACCESS-CM2 shows a stronger than observed thermocline feedback. The implications of this result will be discussed in the presentation.

  3. Audience
    Researchers interested in climate variability, seasonal predictions, climate modelling, and users of the ACCESS model.

  4. Keywords
    ACCESS, climate variability, seasonal predictions, climate modelling


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