ORCA12 configurations

Dear all,

At UCLouvain we are aiming at producing a stand-alone (ERA5-forced or similar) ocean-sea ice simulation covering the satellite era (1979-now) by the end of this year. Currently, we have NEMO4.0.7 configuration running at ORCA1 and we are about to start the tests at ORCA12 with the same version. If resources permit, we might also run an ORCA12 run with NEMO4.2 at some point.

This topic is opened to share experience with those specific configurations. More specifically:

  • Are there standard ocean and sea ice namelists that already exist for this resolution and this model version; if not, are there NEMO3.6-equivalent namelists for ORCA12 we could use?

  • Has anyone bad or good experience with ERA5? has the DFS5.2 been updated / is it still supported and recommended ?

  • Any advice / experience to work around the long spin-up required to equilibrate the model? Do you recommend doing a cold-start?

We’ll be more than happy to share our results, experience bugs, and (sea ice) namelists once we have reached a state that we consider is reasonable :slight_smile: .


At NOC we have a traceable pair of runs using the UK GO8p7 configuration (basically NEMO v4.0.4 with some relatively minor modifications) at 1/4° and 1/12° that have run with JRA-55 forcing from 1958 until the end of 2021. We are just putting together some plans to give us the capacity to bring these runs up to date on a rolling basis as JRA-55 is updated.

I don’t know if I can answer your question about spin-up directly, but our runs start twenty years earlier than your period of interest, and at both resolutions the AMOC has stabilised reasonably well after this time - certainly it has less of a spin-up transient than we have seen with CORE2 or DFS5.2 forcing.

We have also done a shorter run of NEMO v4 with ERA5 and compared this with the same configuration with CORE2, DFS5.2 and JRA-55 forcing. This looks quite similar to JRA-55.

It would be good to keep up communications on this.


Regarding the spinup, I think it depends a lot on the motives of your simulation. Maybe starting from the same initial state as Alex’s simulation would be helpful. It will reduce the degrees of freedom if you want to try to compare simulations.

I know Jean-Marc has also run an eORCA12 v4.0.x simulation, starting from January 1979 and forced with JRA55.

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Hi Alex,

Thanks for picking up the comment and for letting us know about your plans. It’s good to know that the atmospheric forcing does not fundamentally change the results and that you manage to get a reasonable AMOC.

It would help us much if we could use your ocean and sea ice restarts (say 19791231) from your 1/12° JRA55 run. Also, if you can share the two config namelists with us, that would be fantastic. As said we’ll be happy to feedback on any experience and any result we obtain, especially on the sea ice namelists.

I did not mention in my initial message but we have recently developed a sea ice evaluation toolbox that is CMIP6-compliant and can be used on the NEMO sea ice output:

Lin, X., Massonnet, F., Fichefet, T., & Vancoppenolle, M. (2021). SITool (v1.0) – a new evaluation tool for large-scale sea ice simulations: Application to CMIP6 OMIP. Geoscientific Model Development, 14(10), 6331–6354, doi:10.5194/gmd-14-6331-2021

with the GitHub repo:

All the best,

Hi Francois,

You could find here the eORCA025 namelist and the changes for eORCA12 used for the GO6 (3.6 based) simulations used in Storkey et al., 2018:

For input file, the best is probably to ask Jean-Marc (@molines), @DaveStorkey (Met-Office) or @Alex (NOC)


Hi Pierre,
Excellent thank you!