Providing atmospheric N2O for non-interactive-N2O hist sim

[jmaerz]

Hi @TomasTorsvik and @JorgSchwinger , this is a PR to introduce the capability to provide historical atmospheric N2O concentrations in non-interactive-N2O simulations in the iHAMOCC-enhanced release-1.6 branch (to be run in NorESM2.0.x with MCT). For now, it is handled similar to CFCs. I still need to test it on betzy, but in the 1D setup, the correct value is chosen, when switched on.

For using the historical N2O atmospheric concentrations: ./xmlchange HAMOCC_N2O_HIST=TRUE

I think for the purposes that I need it, this should be fine, while I am uncertain, if I should port this also to the master branch (i.e. for ocean-standalone simulations). Let me know, what you think about it. I am not familiar with CAM - but at some point, it might make sense to have a prognostic and diagnostic N2O (and potentially NH3) capability in NorESM3.

@TomasTorsvik , once merged, could you provide a new tag (v1.6.13, if I am not mistaken).

[JorgSchwinger]

Looks good to me. I would vote for including this into master for use in NorESM3! Would be nice to run the historical simulation with this, wouldn't it?

[jmaerz]

Hi @JorgSchwinger thanks for the fast response - yes, that would be my intention (crossing fingers in terms of response of the N-cycle...). Once checked in NorESM2, I will then provide it to master as well.

[TomasTorsvik]

@jmaerz - Thanks for making the PR! I can tag once you ave merged it.

[jmaerz]

Hi @TomasTorsvik and @JorgSchwinger , I now performed a simple hybrid test run with compset NHIST based on a CMIP6 N1850 restart file and ran (job is still running, but with correct results showing up in the monthly output) two years in a NorESM2.0.9 version, switching on ./xmlchange HAMOCC_N2O_HIST=TRUE. I hence merge this now.

[TomasTorsvik]

@jmaerz - I have now made a v1.6.13 tag from this PR.

[jmaerz]

Many thanks @TomasTorsvik! - this is helpful and will find application the next days.