ACCESS-OM3 development highlights/updates

COSIMA Working Group
1

These are presented fortnightly at COSIMA meetings.

First, some context

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

2

2026-02-12

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

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

Call out for missing diagnostics:

3

2026-03-05

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

Request diagnostics for new run:

Other ACCESS-OM3 development

ACCESS-OM2

  • new release soon: WOMBAT-lite and GCC compiler support
5

2026-04-02

ACCESS-OM3 evaluation update

6

2026-04-16

3rd ACCESS-OM3 25km IAF 1958-2023 test run

  • currently underway; details here
  • currently simulating 2008; should be finished (to end of 2023) by early next week
  • data: /g/data/ol01/outputs/access-om3-25km/MC_25km_jra_iaf+wombatlite-test3v2-00532b88

many of the problems highlighted in the last update are now resolved or much improved in the new run :tada:

  • reverted to previous MOM6 and CICE6 code to sidestep still-unresolved mediator NaN bug
  • SSS restoring limited by MAX_DELTA_SRESTORE = 1.0 psu (rather than 0.5 psu, to avoid error)
  • no crashes so far :crossed_fingers:
  • B-grid compatible land mask in polar regions has prevented unbounded ice and snow thickness growth. Thickest ice is <50m thick rather than 10km. Still thicker than OM2, but this would probably be reduced further by spreading solid runoff and associated latent cooling of the ocean.
  • Improved GM parameters have significantly reduced abyssal temperature drift
  • Indonesian throughflow has been improved by topography edits
  • Constricting Bosporus has greatly reduced Black Sea and eastern Mediterranean SSS bias
  • WOMBAT-lite BGC is looking good - @pearseb tells me
    • Chlorophyll looks amazing
    • CO2 flux and iron limitation look great
    • Surface nitrate looks great, but surface iron is too high in coastal areas. Not sure why it’s not being removed rapidly at those concentrations.
    • Vert integrated NPP much too high in a weird place in the Amazon outflow. Otherwise it looks great. However, the weird high values are causing globally integrated rates of NPP that are 3x higher than the median estimate from observations. And much higher than what is considered reasonable.
    • Zooplankton is too low.
7

2026-04-30

3rd ACCESS-OM3 25km IAF 1958-2023 test run

  • 66-year IAF cycle completed
  • includes WOMBAT-lite BGC
  • details here
  • data here: /g/data/ol01/outputs/access-om3-25km/MC_25km_jra_iaf+wombatlite-test3v2-00532b88
  • we welcome analysis/scrutiny of this data - especially the BGC output

Some current ACCESS-OM3 development issues

8

2026-05-14

Good news :tada:

9

2026-05-28

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2026-06-11

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2026-06-24

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2026-07-09

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2026-07-23

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2026-08-06

  • 100km MOM6-CICE6-WW3 OM3 nearing release
  • 100km MOM6-CICE6-WW3 OM3 load balancing complete
  • 25km + 100km OM3 performance optimisation underway - gains of ~10% with MOM6 code changes and compiler directives
  • implementation of river runoff spreading nearing completion
  • code changes underway (splitting JRA55 runoff into river and basal melt) to allow basal melt to be input at depth, also accounting for latent heat
  • 25km OM3 test4 assessment (all the evaluation for the latest ACCESS-OM3-25km test4 run here) highlights areas that need improvement (details here)
    • thermocline too deep,
    • weak southern hemisphere heat transport,
    • SSS too fresh,
    • poor Kuroshio and Gulf Stream separation and variability distribution,
    • incorrect North Atlantic deep convection locations,
    • weak and declining NADW,
    • excessive Mediterranean outflow.
15

2026-08-20

  • river runoff spreading implemented
  • basal melt latent heat being implemented, including distribution of meltwater/cooling at depth; distribution of frazil brine will be considered as a later step.
  • 25km OM3 test4 assessment continuing - please join in to ensure that the model will work well for your areas of interest!
  • 25km OM3 test5 in preparation
    • C-grid CICE
    • horizontal runoff spreading
    • basal melt latent heat
    • numerical mixing diagnostic
    • bathymetry fixes
    • tripole fixes
    • code updates, bug fixes, performance optimisations, etc.
  • WOMBATmid code and documentation complete; parameter optimisation underway
  • Method for cycling OM3 runs under development
  • MCW 100 km ERA5 config: aiming for a beta release; long-run underway, to be presented at AARC next week (slide).
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2026-09-03

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2026-09-14

Development

Evaluation

3 evaluation tasks open to being picked up:

  • Add lines for ACCESS-OM2-01 (IAF cycle 1) to time series of global averages: temperature, salinity, sea surface temperature, sea surface salinity. Modify code here. GH Issue
  • Arctic sea ice analysis (see sea ice plots below mentioning Arctic).
  • Arctic transects in Transects.ipynb to explore the vertical extent of the SSS biases. Just use grid-aligned transects (which won’t be zonal or meridional, due to tripolar coordinates).

Feel free to assign yourself in this post and ask @aekiss or @cbull for access to repository (you’ll need to do this first).