Experiment title 
: ACCESS-ESM1.5 Pacific Warming AMIP Experiments
Summary :
Following our recent Pacific zonal SST warming pattern AMIP experiments in ACCESS ESM1.5, we plan to run a set of new experiments with the hemispheric warming uncertainty and its interactions with plausible zonal warming patterns. These experiments will provide a complete understanding of the role of Pacific warming uncertainty in the future climate.
Scientific motivation:
Observed SST trends over recent decades indicate that the tropical western Pacific warmed more than the eastern Pacific, leading to a strengthened equatorial zonal SST gradient (Lee et al. 2022). In contrast, the majority of CMIP models simulate a reduced zonal SST gradient, with more warming in the eastern Pacific (Cai et al. 2021; Wills et al. 2022; Bai et al. 2023). This discrepancy represents one of the major sources of uncertainty in future tropical climate projections as global atmospheric circulation and regional hydroclimate strongly depend on Pacific variability.
Resolving the causes of this disagreement between observation and climate models will require continued advances in the models and improved understanding of the relative roles of externally forced change and internal climate variability on future Pacific warming pattern evolution. However, an important and more immediate question is how uncertainty in the Pacific warming pattern translates into uncertainty in future rainfall projections. Quantifying this relationship would provide valuable information for policymakers by identifying the extent to which regional hydroclimate projections depend on plausible alternative Pacific warming scenarios.
To address this question, we will perform a set of atmosphere-only ACCESS-ESM1.5 experiments by varying the tropical Pacific warming pattern from the observed La Niña-like trend to the El Niño-like warming projected by many CMIP6 models. In addition, we will investigate uncertainty associated with hemispheric warming asymmetry and its interaction with alternative Pacific zonal warming patterns. Together, these experiments will quantify the climate impacts of plausible future Pacific warming states and provide new insight into the physical drivers of uncertainty in global and regional hydroclimate projections under climate change.
Experiment Name : pac_warm_amip_esm1.5
People : Abhik Santra, in collaboration with Shayne McGregor and others.
Model: ACCESS-ESM1.5
Configuration: AMIP-style simulations with prescribed SST perturbations
Initial conditions: /g/data/k10/sza565/access-esm/restart/restart_1994
Run plan: 21 years per experiment, with 5 ensemble members for each experiment.
Simulation details: A set of sensitivity experiments will be conducted using prescribed SST patterns with varying meridional SST gradients. Ideally, four distinct gradient magnitudes will be tested in each case. In addition to that, a combination of both zonal and meridional gradient experiments will be conducted to better understand the contribution of the predominant modes of the Pacific warming pattern uncertainty.
Total KSUs required : Based on our earlier CPU usage, we need ~1.5 MSU (15 experiments x 5 ensemble members x 21 years) in Q3 2026.
Total storage required : 10.5 TB (15 experiments x 680GB) on gdata/lg87.
Storage lifetime : next 2 years, at least.
Long term data plan : model outputs will be transferred to MDSS (tape).
Outputs: standard monthly variables will be stored on /g/data/lg87/sza565/Pac_Warming_expt/
Restarts: will be available every 5 years.
Related articles:
Analysis:
To be updated.
Conclusion:
Quantifying the rainfall uncertainty associated with Pacific warming pattern uncertainty would provide valuable information for policymakers by identifying the extent to which regional hydroclimate projections depend on plausible alternative Pacific warming scenarios, thereby improving the interpretation and use of climate projections for adaptation and risk assessment.