Hello,
I have noticed that when we retrieve data from the climate data store or from the API, netCDF files use the CF-1.6 conventions. However, when we want to retrieve data from the CDS Toolbox it uses the CF - 1.7 conventions.
Example :
File from the form of the CDS or a CDS API request :
<xarray.Dataset>
Dimensions: (longitude: 1440, latitude: 721, time: 1)
Coordinates:
* longitude (longitude) float32 0.0 0.25 0.5 0.75 ... 359.0 359.2 359.5 359.8
* latitude (latitude) float32 90.0 89.75 89.5 89.25 ... -89.5 -89.75 -90.0
* time (time) datetime64[ns] 2021-01-02
Data variables:
t (time, latitude, longitude) float32 ...
Attributes:
Conventions: CF-1.6
history: 2023-04-05 12:53:19 GMT by grib_to_netcdf-2.25.1: /opt/ecmw...
File from the CDS Toolbox :
<xarray.Dataset>
Dimensions: (lat: 721, lon: 1440)
Coordinates:
realization int64 ...
time datetime64[ns] ...
* lat (lat) float64 -90.0 -89.75 -89.5 ... 89.75 90.0
* lon (lon) float64 -180.0 -179.8 -179.5 ... 179.5 179.8
experimentVersionNumber object ...
Data variables:
t2m (lat, lon) float32 ...
Attributes:
Conventions: CF-1.7
institution: European Centre for Medium-Range Weather Forecasts
history: 2022-08-10T11:59 GRIB to CDM+CF via cfgrib-0.9.9.1/ecCodes-...
source: ECMWF
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There are some differences on these conventions which are disruptive when you want to automate some scripts : the longitude is from 0 to 360 in CF - 1.6 and lon is from -180 to 180 in CF -1.7, the level dimension is in hPa in CF - 1.6 and plev dimension is in Pa in CF - 1.7...
We are currently developing a tool which uses the CDS API, so we're using the CF - 1.6 conventions. Our tool could not work in the future because of a potential change of conventions. I'm pretty sure that we're not the only ones who could be affected by this.
So my questions are :
Will the CDS API use other conventions ?
If the answer is yes :
Could we choose the conventions in the API requests ? :
c = cdsapi.Client() c.retrieve(
'reanalysis-era5-pressure-levels',
{
'product_type': 'reanalysis',
'format': 'netcdf', 'conventions': 'CF-1.6', 'variable': [
'u_component_of_wind', 'v_component_of_wind',
],
'pressure_level': '1',
'year': [
'1992', '1993', '1994'
],
'month': '01',
'day': [
'01',
],
'time': [
'00:00'
],
},
'download.nc') |
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Is there a tool that we can use to change the conventions ?
Kind regards,
Daniel Kuester
1 Comment
Patrick Van Laake
A non-authoritative answer would be that the CDS doesn't concern itself with the CF conventions. It reports the version of the CF conventions that the data producer has used to generate the data file. It is very unlikely that data sets are produced against different conventions for the benefit of the end-users.