ESMF_Scrip2Unstruct workaround

[anntsay]

Requirements

• Reviewed ESMF Documentation
• Searched GitHub Discussions

Affiliation(s)

No response

ESMF Version

v8.9.0

Issue

Getting following error from ESMF_Scrip2Unstruct,

scrip.nc: The units attribute for grid_corner_lon is not degrees nor radians.

My script file structure as follows,

netcdf scrip {
dimensions:
grid_rank = 1 ;
grid_size = 65160 ;
grid_corners = 4 ;
variables:
int grid_dims(grid_rank) ;
double grid_center_lon(grid_size) ;
string grid_center_lon:units = "degrees" ;
double grid_center_lat(grid_size) ;
string grid_center_lat:units = "degrees" ;
double grid_corner_lon(grid_size, grid_corners) ;
string grid_corner_lon:units = "degrees" ;
double grid_corner_lat(grid_size, grid_corners) ;
string grid_corner_lat:units = "degrees" ;
int grid_imask(grid_size) ;
string grid_imask:units = "unitless" ;
int grid_area(grid_size) ;
string grid_area:units = "unitless" ;

// global attributes:
string :title = "Grid with 65160 size" ;
string :conventions = "SCRIP" ;
data:
}

So, I have those attributes. I am not sure why ESMF complains about.

Autotag

@anntsay

[uturuncoglu]

It issue was related to the used engine when the file is written with the xarray under Python like following.

ds.to_netcdf(output_file)

The default engine used in this call depends on the actual Python environment. It could pick h5netcdf, netcdf4 or scipy.

Here are the behaviors of the supported engines:

• h5netcdf:
  It is adding extra type (string) to the variable attributes like seen as following.

    double grid_center_lat(grid_size) ;
    	string grid_center_lat:units = "degrees" ;
  

  and this is triggering issue in the ESMF_Script2Unstruct offline tool since it is using nc_get_att_text() call from netCDF API and having hard time to deal with the attribute.

• netcdf4 and scipy:
  These two engine options are behaving similar. Both options are not adding extra type argument to the variable attributes and producing file like following,

    double grid_center_lat(grid_size) ;
    	grid_center_lat:units = "degrees" ;
  

  Then ESMF_Script2Unstruct offline tool is happy about it and correctly check the attributes of the variable.

It would be nice to explicitly specify the engine that would be used by the xarray ds.to_netcdf() API call. Following options works without any issue,

ds.to_netcdf(ofile, engine="netcdf4")

ds.to_netcdf(ofile, engine="scipy")

[uturuncoglu]

@anntsay please mark as answered if you think there is enough explanation about the issue and suggested solution.