Regrid from an irregular grid by summing

[Aidan (Aidan Heerdegen, ACCESS-NRI Release Team Lead)]

@dougrichardson

ERA5/NCI does not seem to supply the lat/lon bounds, and I’m unsure how I could manually add my own bounds to the irregular lat/lon in pop.

In a different topic @dale.roberts provided a Jupyter notebook that utilised an Iris function guess_bounds that might be useful in your case:

Regridding reanalysis to n48 results in too cold climatology

Hi @pia I’ve had a chance to revisit this a bit today based on @Aidan’s comment. I’ve come up with this notebook which seems to have had the desired effect on the means. The hires and lowres means now match, and they’ve increased to a more reasonable 13-17 degrees C now that the polar grid cells are weighted lower. I acknowledge I’ve probably done this in the least practical way possible, but I’m hoping Cunningham’s Law prevails here and someone else has a better answer.

According to the ESMF docs

• First-order conservative: Preserves the integral of the source field across the regridding. For this method, weight calculation is based on the ratio of source cell area overlapped with the corresponding destination cell area. If the user areas option (see below) is not used, then the areas used in this calculation are those calculated by ESMF and thus the ones for which the conservation holds. The user areas option allows the user to adjust the interpolation weights so that conservation is based on user-supplied areas.

Which sounds like it should sum when regridding. Easy enough to check.