Session 7: Perturbation Experiments in ACCESS-OM2 / Multiple Sensitivity Tests using Experiment Generator & Runner

COSIMA 2025 training program
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:ocean: ACCESS-NRI COSIMA 2025 Training Program

The final session is on this FRIDAY!

Session 7: Perturbation Experiments in ACCESS-OM2 / Multiple Sensitivity Tests using Experiment Generator & Runner

:disguised_face: Presenters: Minghang Li @minghangli , Andrew Kiss @aekiss
:alarm_clock: When: 11am, 29 August 2025 (Friday)
:house: Where: Zoom

:teacher: Description: Modern ocean and climate models like ACCESS-OM2 rely on large, complex forcing datasets (e.g. JRA55-do) to drive simulations. But what if you want to test how sensitive your model is to stronger winds, altered heat fluxes, or reduced storms? Or investigate how uncertain forcing data might affect your results?

This training session introduces perturbation experiments and shows how to create/run them using the ACCESS Experiment Generator and ACCESS Experiment Runner tools. The training will cover:

  • Why perturbation experiments matter for understanding model sensitivity and robustness.

  • How to set up forcing perturbations in forcing.json: forcing_perturbation.pdf (307.3 KB)

  • How to configure and automate multi-run sensitivity tests with the Experiment Generator and Experiment Runner.

By the end of the session, you’ll learn how the ACCESS Experiment Generator and ACCESS Experiment Runner tools make it easy to design and execute multiple sensitivity tests.

:laptop: Prerequisites

  1. Users who have access to Gadi and are members of the vk83 project can load the Payu development environment using, module use /g/data/vk83/prerelease/modules && module load payu/dev

Relevant links:

:date: Interested in full program schedule - Click here for the full program.

If you have any questions, feel free to get in touch with jasmeen.kaur@anu.edu.au and Chris.Bull@anu.edu.au, or ask on the forum.

2025.08.27-perturbation-training.pdf (734.8 KB)

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ACCESS-OM2 Perturbation Experiments – Meeting Notes

Intro

  • Thanks for attending
  • Overview of ACCESS-OM facilities
  • Minghang: new improvements for perturbation experiments

Why Perturbations?

  • Experiments with meltwater, Antarctica, air temperature
  • Study climate change impacts on ocean
  • Storms near poles / extreme events
  • Useful for engineering fixes

ACCESS-OM2 Architecture

  • Forcing data → model
  • JSON config (array of dictionaries)
    • Keys/values: e.g., zonal wind, year
    • Field names = NetCDF variables

Perturbation Approaches

  • Manual (hard)
    • Copy + modify NetCDF files
    • Edit forcing.json
    • Downsides: poor provenance, messy ensembles
  • Online (preferred)
    • Perturbations calculated at runtime
    • Easy ensemble management

Implementation

  • Define data in JSON
  • Must match original spatial/temporal dimensions
  • Supports:
    • Multiple scalings & offsets
    • Temporal ramps
    • Reduced dimensions (1D × 2D → 3D)
  • EOF components & calendar alignment

Minghang Workflow

  • Run physical simulations from GitHub directory
  • Scaling: time-independent 2D / uniform increases
  • Archive / restart management via payu
  • YAML + git handles:
    • Branch creation per perturbation
    • Job submission & tracking
  • Payu ensures reproducibility & retries failed runs

Resources

1 Like
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Feedback:

Sounds like a very nice addition to help run perturbations, thank you!

Thanks for the tutorial, that was great!

Thanks a lot, that was quite interesting. Sorry I have to go. Will the presentation be available?