Experiment title 
: ACCESS-ESM1.5 Pacific Warming AMIP Experiments
Summary :
We propose a suite of AMIP-style experiments using ACCESS-ESM1.5 with prescribed Pacific SST warming scenarios. These experiments are designed to investigate the impacts of alternative Pacific mean-state warming patterns on Australian weather and climate variability under increased greenhouse gas forcing. The focus is on understanding climate responses to Pacific warming structures that differ from those typically simulated by coupled climate models.
Scientific motivation:
Observations over the 20th century indicate that the tropical Pacific has warmed more rapidly in the western basin, while the eastern Pacific has warmed weakly or even cooled, leading to a strengthened equatorial zonal SST gradient (Lee et al. 2022). In contrast, the majority of CMIP-class climate models simulate a reduced zonal SST gradient, with excessive warming in the eastern Pacific (Cai et al. 2021; Wills et al. 2022; Bai et al. 2023).
This mismatch raises a fundamental question: is the observed pattern a forced response that models fail to capture, or is it primarily driven by internal variability? Resolving this uncertainty is critical, as the future evolution of the Pacific mean state has strong implications for climate variability across the globe.
All current Australian climate projections are based on models exhibiting a weaker zonal SST gradient. How these systems respond to an observed-like or enhanced Pacific warming pattern remains largely unexplored. Based on established ENSO-Australian rainfall relationships, a strengthened zonal SST gradient could lead to increased storm activity, enhanced flood risk, and changes in tropical cyclone behaviour. It may also intensify existing rainfall patterns, strengthening wet seasons across Asia and Australia while exacerbating drying trends in other regions.
The proposed experiments aim to quantify the climate impacts of alternative Pacific warming scenarios, providing new insight into Australian climate risks under future warming.
Experiment Name : pac_warm_amip_esm1.5
People : Abhik Santra, in collaboration with Shayne McGregor, Andrea Taschetto, and others.
Model: ACCESS-ESM1.5
Configuration: AMIP-style simulations with prescribed SST perturbations
Initial conditions: To be decided.
Run plan: 25 years per experiment, with a 5-member run for each experiment.
Simulation details: The present-day control simulation commenced in December 2025.
A set of sensitivity experiments will be conducted using prescribed SST perturbations with systematically varied zonal and meridional SST gradients. Ideally, five distinct gradient magnitudes will be tested for each case.
Each experiment will consist of approximately 25-year simulations with five ensemble members, allowing robust assessment of the forced response relative to internal variability. These experiments are planned for completion during Q1–Q2 2026.
If time and computational resources are available, an additional set of experiments may be undertaken in which zonal and meridional SST gradients will be combined in the lower boundary condition to assess potential nonlinear interactions.
Total KSUs required : ~2 MSU (15 experiments × 5 ensemble members × 25 years × 1.1 KSU)
Total storage required : ~25 TB. Temporary storage with final data archived on k10.
Storage lifetime : next 2 years, at least.
Long-term data plan : model outputs will be transferred to MDSS (tape).
Outputs: standard monthly variables following the AMIP suite STASH.
Restarts: will be available every 5 years.
Related articles:
Analysis: To be updated.
Conclusion: