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

[Dani Jones]

Hi Oliver,

You've found the error! Well spotted. By changing `field_lat_inc = 0.25` to
`field_lat_inc = 249*0.25` throughout, where Ny=249 is the number of
latitude points in my ERA5 subset, I was able to get sensible-looking EXF
diagnostics output.

I am still a bit surprised that using a regridded dataset didn't fix my
issue, though. I was thinking that I could regrid the ERA5 data onto the
model grid, comment out the interpolation-related grid parameters in
`data.exf`, and use the default values. Oddly, this didn't work. I might do
some more tests on this later, but for now I'm happy to have something that
runs.

Thanks again!

Best wishes,
Dan(i)


On Thu, Feb 9, 2023 at 3:34 PM Oliver Jahn <jahn at mit.edu> wrote:

> Hi Dan,
>
> I noticed one thing in your data.exf: there is only 1 value for
> vwind_lat_inc which is an array.  You have to provide vwind_nlat-1 values.
> (This is needed for things like Gaussian grids but definitely could use
> more coverage in the docs!)
>
> Oliver
>
>
> On 2023-02-09 09:16, Dani Jones 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
> > <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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