Hello all,
I am looking for the best approach to describe in a CF compliant way the tripolar grids usually used in NEMO configurations.
Basically, the difference with a usual bipolar grid (north pole-south pole) is that the north pole is split into 2 poles moved over Canada and Russia (to have distortions/singularities not over the ocean). A good visual representation can be found here:
http://www.geomar.de/typo3temp/pics/globe_grid2_14_b8edb639ae.png
everything south of the green line (40degN) is identical to a regular grid, but everything north of it is computed using a technique described here:
Madec, G. and M. Imbard, 1996 : A global ocean mesh to overcome the north pole singularity. Clim. Dyn., 12, 381?388.
The usual NEMO output of the grid looks like this:
float longitude(y, x) ;
longitude:standard_name = "longitude" ;
longitude:units = "degrees_east" ;
longitude:long_name = "longitude" ;
float latitude(y, x) ;
latitude:standard_name = "latitude" ;
latitude:units = "degrees_north" ;
latitude:long_name = "latitude" ;
Basically both latitudes and longitudes need to be specified for each grid point, hence lat and lon are 2D arrays. This is not a problem itself but I would like to give more information through maybe grid_mapping or crs so it is clear that the grid is tripolar. This is useful information if one want to project/interpolate this back to a more regular representation.
Looking at the CF conventions, I can see that grids can be fairly nicely documented but nothing for tripolar grids.
Is there some documentation/guidelines on how to derive a proper grid_mapping/crs with valid attributes for tripolar grids?
I would also like to add to my netcdf file a way to better describe axes:
double y(y) ;
y:units = "1" ;
y:long_name = "j-index of mesh grid" ;
y:standard_name = ??? ;
double x(x) ;
x:units = "1" ;
x:long_name = "i-index of mesh grid" ;
x:standard_name = ??? ;
what would be the standard name of these?
Thanks,
____________________________________
Dr. S?bastien Villaume
Analyst
ECMWF Shinfield Park,
Reading RG2 9AX, UK
+44 7825 521592
sebastien.villaume at ecmwf.int
____________________________________
Received on Thu Mar 30 2017 - 09:52:56 BST
