Change grid_type = 'setmask' to use kmt_type instead (NUOPC / CMEPS)

[apcraig]

This came from #660.

[dabail10]

This is tricky, and I would like some discussion about this. The logic here is that when we are in prescribed ice mode, we want to read the grid and mask information from the mesh file and not from the "grid/kmt" file. So, this is not just kmt. So, maybe the string is not clear. Maybe it should be 'setgrid'? Or 'meshgrid'? Otherwise if we are not in prescribed mode, we read the grid and kmt file and check the lat/lon/mask against the mesh file.

[dabail10]

Thoughts on this? @apcraig @eclare108213 @DeniseWorthen

[DeniseWorthen]

@dabail10 I'm not sure this change would impact us since we always run grid_type='tripole'. For UFS, we don't have a prescribed ice mode; like you say, we read the grid and kmt file and check it is consistent w/ the mesh file.

[apcraig]

Are you proposing we add a mode where instead of grid/kmt, CICE could read a mesh file? I don't think we want to use grid_type for that. grid_type still needs to be dispaced or tripole or whatever, even if a mesh is read. Lets say a mesh could also be used from non-prescribed cases, that's how we'd want it to be able to work. I would use grid_format and set it to meshnc or something like it. So, grid_file sets the mesh filename, grid_format=meshnc, grid_type is still as now. Would that work?

[dabail10]

I like this idea.

[DeniseWorthen]

We create the mesh for MOM6/CICE6 by first creating a SCRIP file (from the MOM6 supergrid) and converting that to an ESMF mesh using ESMC_SCRIP2unstruc. Similarly, for a rectilinear global or regional grid, it is trivial to create a SCRIP file using netCDF operators. So, would it be more general to allow the reading of a SCRIP file rather than a mesh file? In either case (reading SCRIP or mesh), you need the mask (kmt) information added to the file or else you'll still need to have the kmt file read.

[dabail10]

This brings up another issue that is out there. We really need to add an option to read the MOM6 supergrid directly instead of requiring this conversion to kmt/grid files. I don't think we want to add a capability to read SCRIP grid files. The mesh files are the new NUOPC requirement. As you highlighted, when we run in prescribed ice mode, we are using only the mesh file and do not use the kmt/grid files.

[apcraig]

That all sounds reasonable. We can implement whatever we need and can add quite a bit of flexibility. We could add

• mesh including kmt
• mesh + separate kmt file
• scrip + kmt file
• mom supergrid

and some additional options for prescribed grid if that's a special case. You just need to decide what you want to support. They could all be added via various grid_format settings.

[DeniseWorthen]

I'm a little confused why this is listed as a NUOPC/CMEPS issue vs a general issue about possible file formats CICE itself could read to create the grid.

[dabail10]

I think it started out that way because 'setmask' was a NUOPC/CMEPS issue only. However, I agree that it is kind of growing beyond this. I am going to submit a PR to fix this issue and then we can start another about more general grid/kmt handling.