nedclimaterisk
New member
Not sure if this post is in the right place, please move it if not.
I have a WRF output dataset from the NARCliM project, and am trying to use the data by using the rotated pole specs, but the grid is not lining up.
The grid specifications from the WPS file supplied by the NARCliM team is this:
As far as I can work out, this should use the rotated pole lat/lon of 60.31/141.38 - this is the same rotated pole as the CORDEX AUS-44 domain. That's what the actual dataset says too, the rotated ole spec in the netcdf file is:
However, plotting the data with that grid results in this plot (using cartopy and xarray):
https://imgur.com/luxOiqc
The data is significantly mis-aligned - it's off by about 85km near Adelaide.
By trial and error, I've found that this rotated pole gets very close:
https://imgur.com/g5bzB6P
However, these numbers don't seem to correspond to anything in the namefile, and moving that 5.1° shift into the pole_longitude results in a significantly worse projection. I have tried as many other combinations of the geogrid latlon spec in the cartopy RotatedPole as I can think of, and none of them provide reasonable results.
I should note that the actual lat/lon values in the output (as opposed to the rlat/rlon values) are correct - plotting a scatter plot using the lat/lon values instead of the grid results in points that are in the right place according to the coastlines. But this isn't useful for my purposes, ans I need to interpolate between grid points in xarray, and for that I need to use the rlat/rlon grid.
I'm not sure if this is something to do with a mis-specified pole, a bug in WRF or Cartopy, or something else. The NARCliM authors tell me that there wasn't any post-processing done on the grid.
Does anyone know what I might be doing wrong, or what might cause this problem?
I have a WRF output dataset from the NARCliM project, and am trying to use the data by using the rotated pole specs, but the grid is not lining up.
The grid specifications from the WPS file supplied by the NARCliM team is this:
Code:
&geogrid
parent_id = 1, 1,
parent_grid_ratio = 1, 5,
i_parent_start = 1, 82,
j_parent_start = 1, 36,
e_we = 216, 326,
e_sn = 145, 201,
geog_data_res = '10m','2m',
dx = 0.44
dy = 0.44
map_proj = 'lat-lon',
ref_lat = -24.26,
ref_lon = 147.63,
pole_lat= 60.31
pole_lon= 321.38
stand_lon = 32.37,
geog_data_path = '../../DATA/geog'
/As far as I can work out, this should use the rotated pole lat/lon of 60.31/141.38 - this is the same rotated pole as the CORDEX AUS-44 domain. That's what the actual dataset says too, the rotated ole spec in the netcdf file is:
Code:
Attributes:
grid_mapping_name: rotated_latitude_longitude
dx_m: 9783.618
dy_m: 9783.618
grid_north_pole_latitude: 60.31
grid_north_pole_longitude: 141.38However, plotting the data with that grid results in this plot (using cartopy and xarray):
Code:
crs_map = ccrs.PlateCarree()
rotated_pole_n = ccrs.RotatedPole(141.38, 60.31)
ax = plt.axes(projection=crs_map)
ax.coastlines()
dsn.tasmax.plot(ax=ax, transform=rotated_pole_n,
cmap='inferno', alpha=0.5)https://imgur.com/luxOiqc
The data is significantly mis-aligned - it's off by about 85km near Adelaide.
By trial and error, I've found that this rotated pole gets very close:
Code:
rotated_pole_n = ccrs.RotatedPole(
147.38, 60.6,
central_rotated_longitude=5.1)https://imgur.com/g5bzB6P
However, these numbers don't seem to correspond to anything in the namefile, and moving that 5.1° shift into the pole_longitude results in a significantly worse projection. I have tried as many other combinations of the geogrid latlon spec in the cartopy RotatedPole as I can think of, and none of them provide reasonable results.
I should note that the actual lat/lon values in the output (as opposed to the rlat/rlon values) are correct - plotting a scatter plot using the lat/lon values instead of the grid results in points that are in the right place according to the coastlines. But this isn't useful for my purposes, ans I need to interpolate between grid points in xarray, and for that I need to use the rlat/rlon grid.
I'm not sure if this is something to do with a mis-specified pole, a bug in WRF or Cartopy, or something else. The NARCliM authors tell me that there wasn't any post-processing done on the grid.
Does anyone know what I might be doing wrong, or what might cause this problem?