[MITgcm-support] Problems with the EXF package and binary input files

[Gus Correa]

Good morning Dani

May I ask why you are regridding the data for use by the EXF package?
My recollection is that it does on the fly grid interpolation, which is
probably the best feature of EXF.
Here is what the documentation says:
https://mitgcm.readthedocs.io/en/latest/phys_pkgs/exf.html
"An interpolation routine provides on-the-fly interpolation of forcing
fields an arbitrary grid onto the model grid."
Check the EXF package CPP options that enable this interpolation also (link
above).
You probably need the CAL package to get the timing right.

You may still need to convert to binary format (say, if not using
netCDF/MNC package,).
If using the MDS package for IO, you still need swap bytes (it stuns me
that MITgcm continues to insist in big-endian),
if needed, ensure that lat,lon,lev,time go in the correct order, create
consistent data.exf  and data.cal namelists, etc.
I believe there are some Matlab routines in the MITgcm tarball that may
help to convert to binary.

My two cents,
Gus Correa




On Thu, Feb 9, 2023 at 9:17 AM Dani Jones <dcjones.work at gmail.com> wrote:

> Hello MITgcm-support listers,
>
> I am having trouble with the EXF package while trying to force a regional
> model configuration using external fields derived from ERA5. The
> diagnostics output from EXF shows horizontal stripes or distorted results.
>
> To set up my configuration, I followed these steps:
>
>    - Downloaded a subset of ERA5 using the cdsapi package
>    - Regridded the data onto my model grid using the xESMF package
>    - Ran MITgcm for a few timesteps and checked the EXF diagnostics
>    output
>
> I have conducted various checks and tried different approaches to resolve
> the issue, including:
>
>    - Examined the contents of the ERA5 data
>    - Examined the binary files for any problems
>    - Tried "on the fly" interpolation with EXF and repeatedly checked the
>    data.exf parameters
>    - Checked the precision and endian-ness throughout the entire process
>    - Created binary files using Matlab and Python
>    - Updated to the latest version of MITgcm and recompiled with the
>    -D_BYTESWAPIO flag
>    - Tried every permutation of the dimensions for the binary files
>
> Despite these efforts, the binary files appear to be fine, and it seems
> that MITgcm/EXF is not reading them as expected. For further information
> and details, I have documented this issue on GitHub with plots from the
> diagnostics package and links to relevant files:
>
> https://github.com/so-wise/so-wise-gyre/issues/34
>
> Thanks in advance for any assistance, guidance, or suggestions that you
> can provide.
>
> Best regards,
> Dan(i)
>
> --
> *Dr Dan(i) Jones* • Physical Oceanographer
> Polar Oceans Team <https://www.bas.ac.uk/team/science-teams/oceans/> • BAS
> AI Lab <https://www.bas.ac.uk/project/ai> • British Antarctic Survey
> <https://www.bas.ac.uk/>
> Website <http://www.danjonesocean.com/> • Twitter
> <https://twitter.com/DanJonesOcean> • they/them
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