[MITgcm-support] exch2 and autogenerated grids (llc, cs, etc.)

[Jean-Michel Campin]

Hi Ryan,

There might be some confusion here:
1) this part of the documentation:
> http://mitgcm.org/public/r2_manual/latest/online_documents/node233.html
 is NOT up-to-date. No need to use any matlab script (driver.m) from 
 MITgcm/utils/exch2/matlab-topology-generator to set-up the correct/customized
 exch2 topology. See the top of the 2 README files 
 in: utils/exch2/matlab-topology-generator and in: utils/exch2/code-mods

 Setting SIZE.h and data.exch2 should be enough to get pkg/exch2 tile-topology
 set-up.
 But this is (mostly) independent from the the input grid-files
 which provides lat,lon position, grid-spacing and grid-cell area.

2) Regarding grid files (horizGridFile= ...) used with usingCurvilinearGrid=T,
 I am not aware of any MITgcm fortran code that would generate these files.
 Some set of grid-files are available (in some verification exp., also in 
 MITgcm_contrib area) but otherwise you will need to generate these files.
 There has been few email exchange on support list related to how generate 
 grid-files for cubed-sphere grid ; and you can take a look at the recently
 publish paper in GMD about ECCO-v4, with some information regarging the 
 lap-lon-cap grid and grid-files.

Cheers,
Jean-Michel
 
On Thu, Oct 22, 2015 at 05:16:17PM -0400, Ryan Abernathey wrote:
> Hi,
> 
> After avoiding this issue for a long time, I am finally trying to
> understand how the new auto-generated grids work (in particular the llc
> grids).
> 
> Is this documentation up to date?
> http://mitgcm.org/public/r2_manual/latest/online_documents/node233.html
> 
> For the global_oce_llc90 setup, the input files seem very simple, i.e. data
> file just has
>   usingCurvilinearGrid=.TRUE.,
> 
> and data.exch2 has
>   W2_printMsg= 0,
>   W2_mapIO   = 1,
>   preDefTopol=0,
>   dimsFacets(1:10) = 90, 270, 90, 270, 90, 90, 270, 90, 270, 90,
>   facetEdgeLink(1:4,1)= 3.4, 0. , 2.4, 5.1,
>   facetEdgeLink(1:4,2)= 3.2, 0. , 4.2, 1.3,
>   facetEdgeLink(1:4,3)= 5.4, 2.1, 4.4, 1.1,
>   facetEdgeLink(1:4,4)= 5.2, 2.3, 0. , 3.3,
>   facetEdgeLink(1:4,5)= 1.4, 4.1, 0. , 3.1,
> 
> This is evidently enough information to completely specify the grid
> geometry. But I can't figure out where in the code the geometry is actually
> calculated. In ini_curvilinear_grid.F, it looks like it is just reading the
> geometry from horizGridFile (i.e. tile.0001.mitgrid). So when do these
> horizGridFiles get written?
> 
> Just looking for some hints to get started on understanding this important
> but intimidating subject.
> 
> Thanks,
> Ryan

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