ACCESS-OM3 development highlights/updates

[aekiss (Andrew Kiss)]

These are presented fortnightly at COSIMA meetings.

First, some context

• ACCESS-OM3 is a multi-resolution suite of global ocean-sea ice models under development by ACCESS-NRI and the COSIMA community
  • The successor to ACCESS-OM2, upgrading to MOM6 and CICE6 and updating configuration settings and inputs
  • coordinated development with CM3/ESM3 (get involved here) and regional MOM6
  • initial focus on 25km (0.25°) for CM3
  • higher resolution (8km) in early development
  • optional WOMBAT BGC
  • optional 2-way wave-ocean and wave-ice coupling in development
  • options for ice shelf cavities planned, building on mom6-panAn-iceshelf
• ACCESS-OM3 documentation
• ACCESS-OM3 configurations
  • different configs (resolution, IAF/RYF, BGC) are under branches
    • rel-* : releases (announced here)
    • dev-* : under development; see project board
• ACCESS-OM3 executable source code
  • look up sources for code releases here
• ACCESS-OM3 test runs
• ACCESS-OM3 assessment scripts and discussion (in issues)
• Technical Working Group (TWG) meeting announcements and minutes

[This is a wiki post - free free to edit.]

[aekiss (Andrew Kiss)]

2026-02-12

Working towards next IAF 25km test configuration and 66-year run

• Differences so far: Comparing release-MC_25km_jra_iaf..dev-MC_25km_jra_iaf · ACCESS-NRI/access-om3-configs · GitHub
• Improvements to GM and Redi parameters GM parameters in OM3 · Issue #1100 · ACCESS-NRI/access-om3-configs · GitHub
• Improve Indonesian topography (hopefully improving throughflow) Tweak 25km topography in Indonesian straits · Issue #879 · ACCESS-NRI/access-om3-configs · GitHub
• Make polar coastlines compatible with B-grid CICE to hopefully avoid unrealistic ice thickness buildup Time series of running 12-month minimum, mean and maximum sea ice extent and volume · Issue #20 · ACCESS-Community-Hub/access-om3-paper-1 · GitHub
• Improve representation of bottom roughness for parameterisation of internal tides Parameterize impact of tides · Issue #457 · ACCESS-NRI/access-om3-configs · GitHub

Also working on (maybe not ready for the next run)

• Spreading iceberg fluxes (water and latent heat) to reduce unrealistic ice thickness - Calving flux via iceberg distribution map · Issue #404 · ACCESS-NRI/access-om3-configs · GitHub . Planning to use Merino climatology for spreading of Antarctic fluxes - looking for recommendations for spreading pattern for Greenland

Call out for missing diagnostics:

• Diagnostics changes for next ACCESS-OM3 25km release · Issue #1046 · ACCESS-NRI/access-om3-configs · GitHub

[aekiss (Andrew Kiss)]

2026-03-05

Continuing work towards next ACCESS-OM3 IAF 25km test configuration and 66-year run:

• improved Indonesian topography, GM, bottom roughness (see above)
• WOMBAT-lite BGC
• SSS restoring is excessive Maps and timeseries of SSS restoring · Issue #44 · ACCESS-Community-Hub/access-om3-paper-1 · GitHub - try to reduce MAX_DELTA_SRESTORE Decrease `MAX_DELTA_SRESTORE` in 25km and finer · Issue #1180 · ACCESS-NRI/access-om3-configs · GitHub, but sources of SSS biases also need addressing, e.g.
  • high sea ice production rates, e.g. off eastern Siberian coast Excessively low T and high S in 0.25 degree · Issue #325 · ACCESS-NRI/access-om3-configs · GitHub
  • high sea ice production due to latent heat extraction concentrated at the coast when there’s no lateral spreading of the iceberg calving meltwater Calving flux via iceberg distribution map · Issue #404 · ACCESS-NRI/access-om3-configs · GitHub ; iceberg flux lateral spreading code is in development Regrid iceberg fluxes on OM3 grid by anton-seaice · Pull Request #120 · ACCESS-NRI/om3-scripts · GitHub
  • insufficient lateral and vertical spreading of river outflows Runoff redistribution · Issue #396 · ACCESS-NRI/access-om3-configs · GitHub
  • poor western boundary current separation, e.g. Gulf Stream
  • bad straits - eg Bosphorus Restrict Black Sea - Mediterranean flow · Issue #729 · ACCESS-NRI/access-om3-configs · GitHub - try methods to reduce transport C-grid bathymetry and land mask · Issue #262 · ACCESS-NRI/access-om3-configs · GitHub
• ADJUST_NET_SRESTORE_BY_SCALING = True Try ADJUST_NET_SRESTORE_BY_SCALING = True · Issue #260 · ACCESS-NRI/access-om3-configs · GitHub

Request diagnostics for new run:

• Diagnostics changes for next ACCESS-OM3 25km release · Issue #1046 · ACCESS-NRI/access-om3-configs · GitHub

Other ACCESS-OM3 development

• Support for ERA5 forcing (which runs to present day, in contrast to JRA55-do, which ends in early 2024) Swapping from JRA55 to ERA5 atmospheric forcing · Issue #548 · ACCESS-NRI/access-om3-configs · GitHub
• We have no provenance for the 1° ACCESS-OM2 grid, so could not modify it (e.g. extend it further south). So a new 1° (100km) grid workflow is in development, including updates to associated inputs, e.g. topography New OM3 100km grid · Issue #1111 · ACCESS-NRI/access-om3-configs · GitHub

ACCESS-OM2

• new release soon: WOMBAT-lite and GCC compiler support