Hi all, I’m interested in running an ensemble for ACCESS-CM2 - I’ll be perturbing the initial air temperatures by about 10^-13 randomly. There are a few people @ars599 @zoegillett27 @spencerwong who have successfully done this 3 years ago here , @sebmckenna did it 2 years ago here , and most recently…

The default size perturbation is large enough that significant differences appear very quickly. Using a copy of /data/access/access-cm2/cmip6_restarts/bi889/restart/atm/bi889a.da09500101_00 module use ~access/modules module load pythonlib/umfile_utils/access_cm2 perturbIC.py -s 0 bi889a.da09500101…

Have you confirmed the perturbed files are actually different, e.g. by running diff FILEA FILEB or by plotting the perturbed field in each file?

I have no clue if this is important here and I have never done any of these before, but 1e-13 is close to 64-bit floating-point machine precision for temperatures in Kelvin with values ~270: julia> eps(270.0) 5.684341886080802e-14 # <- machine precision for 64-big float value of 270.0 So you might…

another potential approach for debugging, building on the good suggestions that have come before: maybe hit it with a bigger hammer (say, 10**-2, or even 1 for clarity about whether anything changed) and check if that has an impact on the model’s evolution

Hi Joel, In the end I didn’t need an ensemble, so I’m not too sure how that code works. I believe @huazhen has done this recently with ACCESS-CM2 though, so hopefully she can provide more help. I’m interested to know as well. Cheers, Zoe

Thanks all for your replies! @Scott the diff command returns nothing, these files are identical. I even did a histogram of the air temperature differences and got the min, mean, max difference at 15 decimals and still no difference. Is it something to do with the script @tammasloughran ? @Benoit @j…

[image] MartinDix: This worked well, thanks @MartinDix and @jemmajeffree for the help. It seems to be the script I was using was not working correctly, your script accessible with the modules module use ~access/modules module load pythonlib/umfile_utils/access_cm2 works as expected.

Ensemble run for ACCESS-CM2: Perturbations have no effect

Earth System Coupled Model

jemmajeffree (Jemma Jeffree) 16 March 2026 05:05 7

@MartinDix
Am I right in remembering that perturbIC.py is your script? any suggestions or guidelines on how it should be used?

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Ensemble run for ACCESS-CM2: Perturbations have no effect

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