Produce Nitrogen (N2) forcing ancillaries for the ACCESS-ESM1.6 `historical` experiments

[atteggiani]

From the CMIP7 inputs meeting notes of 08.10.2025:

• N2 forcing data is available. @penguian to check if NCI has downloaded this data.
• N2 forcing is a surface field, so we need to interpolate it and make sure it’s non-zero over land.

[MartinDix]

Using FZJ-CMIP-nitrogen-1-1 and comparing CMIP6 and CMIP7 (CMIP7 solid, CMIP6 dashed) shows a strange jump in the CMIP7 drynoy for 1930-39. Solid lines are CMIP7, dashed CMIP6.

[MartinDix]

See PCMDI/input4MIPs_CVs#385

[MartinDix]

[MartinDix]

https://input4mips-cvs.readthedocs.io/en/latest/dataset-overviews/nitrogen-deposition/ says

There were faulty N-deposition values in the 1930s across variables and the variable wetNOy was 50% too high in both the PI and historical forcing fields due to double-counting of some wetNOy components.

The wetNOy term so is now more similar to CMIP6. CMIP7 1-2 is the solid line in both plots.

[MartinDix]

Checking /g/data/tm70/pcl851/CMIP7/esm1p6_ancil/2025.12.19/modern//historical/atmosphere/land/biogeochemistry/global.N96/2025.12.19/Ndep_1849_2023_cmip7.anc

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