grid mapping definitions of CNRM-ALADIN64E1

[larsbuntemeyer]

For example:

int Lambert_Conformal ;
		Lambert_Conformal:grid_mapping_name = "latitude_longitude" ;
		Lambert_Conformal:latitude_of_projection_origin = 49.5 ;
		Lambert_Conformal:standard_parallel = 49.5 ;
		Lambert_Conformal:longitude_of_central_meridian = 10.5 ;
		Lambert_Conformal:false_easting = 0. ;
		Lambert_Conformal:false_northing = 0. ;

@pierrenabat
The grid mapping name here should be lambert_conformal_conic, not latitude_longitude. This will not work with CF compliant tools.

See also this comment

[pierrenabat]

Hello Lars, thanks for pointing out this error, indeed it should be "lambert_conformal_conic", I will correct it

[larsbuntemeyer]

Thanks! It's not a big issue for the evaluation overview, the rest of the grid definition (lon/lat) and bounds seem fine.

[larsbuntemeyer]

@pierrenabat I can make a reasonable plot of CNRM-ALADIN64E1 orography with the following fix (based on HCLIM43-ALADIN grid):

import cartopy.crs as ccrs
import cartopy.feature as cf
import matplotlib.pyplot as plt

import xarray as xr

cnrm  = xr.open_dataset("/mnt/CORDEX_CMIP6_tmp/sim_data/CORDEX/CMIP6/DD/EUR-12/CNRM-MF/ERA5/evaluation/r1i1p1f1/CNRM-ALADIN64E1/v1-r1/fx/orog/v20250116/orog_EUR-12_ERA5_evaluation_r1i1p1f1_CNRM-MF_CNRM-ALADIN64E1_v1-r1_fx.nc")
smhi = xr.open_dataset("/mnt/CORDEX_CMIP6_tmp/sim_data/CORDEX/CMIP6/DD/EUR-12/HCLIMcom-SMHI/ERA5/evaluation/r1i1p1f1/HCLIM43-ALADIN/v1-r1/fx/orog/v20241205/orog_EUR-12_ERA5_evaluation_r1i1p1f1_HCLIMcom-SMHI_HCLIM43-ALADIN_v1-r1_fx.nc")

# fix coordinates, see e.g. SMHI coordinates
cnrm['x'] = cnrm.x * 1000. + 100000. 
cnrm['y'] = cnrm.y * 1000. + 100000.

transform = ccrs.LambertConformal(central_longitude=10.5, central_latitude=49.5, 
                                  false_easting=2924999.9999999995, false_northing=2924999.9999999986,
                                  standard_parallels=(49.5, 49.5),
                                  globe=None, cutoff=-30)

def plot(ds):
    plt.figure(figsize=(10,8))
    ax = plt.axes(projection=transform)
    ax.gridlines(draw_labels=True, linewidth=0.5, color='gray',
                xlocs=range(-180,180,10), ylocs=range(-90,90,5))
    ds.orog.plot(ax=ax, transform=transform, cmap="terrain", vmin=-500, vmax=3000)
    ax.coastlines(resolution='50m', color='black', linewidth=1)
    ax.add_feature(cf.BORDERS)

plot(cnrm)

As you can see, i used grid mapping definitions from HCLIM43-ALADIN (it has definitions of false_easting and false_northing which are missing in CNRM-ALADIN64E1). I also had to convert coordinates to m and add a shift (like inHCLIM43-ALADIN).

@gnikulin: I'm no expert in lambert conformal grids, but to me it seems, that CNRM-ALADIN64E1 should have the same grid definitions as HCLIM43-ALADIN for EUR-12?

see, e.g.,

smhi.crs.attrs

{'grid_mapping_name': 'lambert_conformal_conic',
 'standard_parallel': np.float64(49.5),
 'longitude_of_central_meridian': np.float64(10.5),
 'latitude_of_projection_origin': np.float64(49.5),
 'false_easting': np.float64(2924999.9999999995),
 'false_northing': np.float64(2924999.9999999986),
 'earth_radius': np.float64(6371229.0),
 'proj4': '+proj=lcc +lat_1=49.500000 +lat_2=49.500000 +lat_0=49.500000 +lon_0=10.500000 +k_0=1.0 +x_0=2925000.000000 +y_0=2925000.000000 +a=6371229.000000 +b=6371229.000000'}