NetCDF File with Rotated Lat/Lon Grid Causing Error

[balbrightwpc]

Hello,

I am trying to run pcp_combine on some experimental West-WRF runs we received from a partner that are in netCDF format. When running the command, I receive the following error:

ERROR :
ERROR : NcCfFile::get_grid_mapping_rotated_latitude_longitude() -> Rotated latitude longitude grid not handled in MET.
ERROR :

Here are the ncdump details of one of the netCDF files that are being used (I did not include all variables to save space):

ncdump -h west-wrf_gfs_d02_2023-01-09_12_00_00.nc
netcdf west-wrf_gfs_d02_2023-01-09_12_00_00 {
dimensions:
time = UNLIMITED ; // (1 currently)
west_east = 717 ;
south_north = 753 ;
variables:
double time(time) ;
time:standard_name = "time" ;
time:long_name = "Time" ;
time:units = "hours since 1970-01-01 00:00:00" ;
time:calendar = "standard" ;
time:axis = "T" ;
float lon(south_north, west_east) ;
lon:standard_name = "longitude" ;
lon:long_name = "Longitude" ;
lon:units = "degrees_east" ;
lon:_CoordinateAxisType = "Lon" ;
float lat(south_north, west_east) ;
lat:standard_name = "latitude" ;
lat:long_name = "Latitude" ;
lat:units = "degrees_north" ;
lat:_CoordinateAxisType = "Lat" ;
float west_east(west_east) ;
west_east:standard_name = "projection_x_coordinate" ;
west_east:long_name = "x coordinate of projection" ;
west_east:units = "degrees_east" ;
west_east:axis = "X" ;
float south_north(south_north) ;
south_north:standard_name = "projection_y_coordinate" ;
south_north:long_name = "y coordinate of projection" ;
south_north:units = "degrees_north" ;
south_north:axis = "Y" ;
int Rotated_Pole ;
Rotated_Pole:grid_north_pole_longitude = 180.f ;
Rotated_Pole:grid_north_pole_latitude = 51.f ;
Rotated_Pole:grid_mapping_name = "rotated_latitude_longitude" ;
float precip(time, south_north, west_east) ;
precip:standard_name = "total_precipitation_amount" ;
precip:long_name = "Accumulated Total Precipitation Over Simulation" ;
precip:units = "mm" ;
precip:grid_mapping = "Rotated_Pole" ;
precip:coordinates = "lat lon" ;
precip:_FillValue = 1.e+20f ;
precip:missing_value = 1.e+20f ;
// global attributes:
:CDI = "Climate Data Interface version 2.3.0 (https://mpimet.mpg.de/cdi)" ;
:_NCProperties = "version=2,netcdf=4.7.4,hdf5=1.10.7," ;
:Conventions = "CF 1.6, Standard Name Table v19" ;
:source = "/expanse/lustre/scratch/cw3eprod/temp_project/NRT_gfs_backfill/output/2023010900/wrf_2dom/wrfout_d02_2023-01-09_12_00_00" ;
:institution = "CW3E - Scripps Institution of Oceanography" ;
:title = "/expanse/lustre/scratch/cw3eprod/temp_project/NRT_gfs_backfill/output/2023010900/cf/wrfcf_gfs_d02_2023-01-09_12_00_00_temp.nc" ;
:notes = "Created with NCL script: wrfout_to_cf.ncl v2.0" ;
:created_by = "Daniel Steinhoff - dcw3eprodf@ucsd.edu" ;
:creation_date = "Mon Oct 7 19:07:48 PDT 2024" ;
:history = "Fri Oct 11 11:47:57 2024: cdo -w -L -O merge temp1.nc temp2.nc temp3.nc temp4.nc temp5.nc temp6.nc /expanse/lustre/scratch/cw3eprod/temp_project/NRT_gfs_backfill/output/2023010900/west-wrf_2023010900/west-wrf_gfs_d02_2023-01-09_12_00_00.nc\nFri Oct 11 11:47:34 2024: cdo -w -L -O chname,Z_p,Z500 -setzaxis,surface -sellevel,500 -selname,Z_p wrfcf_gfs_d02_2023-01-09_12_00_00.nc temp1.nc" ;
:CDO = "Climate Data Operators version 2.3.0 (https://mpimet.mpg.de/cdo)" ;
}

Do you have any advice on how to handle this file? If you need any other information or if you need me to upload one of the files, please let me know. Any help would be appreciated, thank you!

Ben Albright

[CPKalb]

Hi Ben:

What version of MET are you using? Support for rotated lat/lon grids was added in MET version 10.1.1. So, the first thing to check is to make sure you are running MET version 10.1.1 or higher.

Assuming you are running 10.1.1 or higher, would you be able to upload a file using the instructions so we can take a closer look?

Thanks,
Christina

[balbrightwpc]

Hi John,

Appreciate the reply and you continuing to look into the issue. I ran into the same issue when trying to plot the data as well after renaming the data. I believe one of my co-workers was able to plot the raw data correctly. I have asked him to either post here or relay to me what he did so stay tuned.

[tomerburg]

Hi all,

The metadata in these files are different than files I normally work with - the 1D coordinates "east_west" and "south_north" are technically in degrees longitude and latitude, respectively, but don't actually correspond to the coordinates of the data. That would be the "lon" and "lat" 2D arrays. When I plotted it with Python/Cartopy, using the "lon" and "lat" arrays as the x and y coordinates, I was able to get the data correctly plotted:

I don't have enough MET expertise to know whether it's a bug on MET's side or with how the data is provided into MET, but hopefully this is enough information to guide you in the right direction.

[CPKalb]

@JohnHalleyGotway, correct me if I'm wrong, but I think MET needs the latitude and longitude for rotated lat/lon grids to be 1d variables. However, from the previous post, those variables don't correspond to the actual data in the file. I ran some testing on this. Specifically, I edited the netCDF file so that the dimensions are lat and lon (rather than west_east and south_north). I also edited the lat and lon variables to have standard name attributes of grid_latitude and grid_longitude. However, the file still does not go through MET. I get the following error:

ERROR  : 
ERROR  : NcCfFile::get_grid_mapping_rotated_latitude_longitude() -> Coordinate variables don't match dimension sizes in netCDF file.
ERROR  : 

I'm guessing you will need to read this file in using a python embedding script, as I don't think it can be read into MET in the format it is currently in.

Tina

[JohnHalleyGotway]

Thanks for the discussion on this. I can confirm that MET really is using the data lat/lon information from the 1D "east_west" and "south_north" coordinate variables to geo-locate this data. It's does not use the 2D lat/lon variables at all. And I believe that MET really is processing this data as it should based on the CF-conventions for Rotated Pole data. I certainly don't see any obvious bugs in the MET code that warrant a bugfix.

There are some CF-compliance checker utilities that you could try out:
https://cfconventions.org/software.html

They might be useful in figuring out how to specify the grid information in a cf-compliant way.

[balbrightwpc]

I appreciate you both taking the time to look into this issue. We are back in contact with our partners that provided the data and are working on a solution to format them differently.

[CPKalb]

Thanks for the update. I'm going to go ahead and close this issue then. Please feel free to start up a new issue if you encounter problems with the newly formatted data files or other MET/METplus issues.

Christina