ERA5 : Try to modify valid_time

Datasets and Usage C3S - Datasets and Usage
1

Hi,
I download data for my team, and until now the variable in the files was time I use bash scripts.

I try to modify valid_time to an integer using ncap2 :
ncap2 -O -h -s “valid_time=int(valid_time)” {RES_REANALYSIS}/{file_fin_monthly} {RES_REANALYSIS2}/{file_fin_monthly_new}

and also to modify the name and the dimension valid_time into time :
ncrename -d valid_time,time -v valid_time,time
${RES_REANALYSIS}/$file_monthly

But it does not work.
If someone knows how to do this ?
Thanks

2

Hello
I tried with NCO but that results in loss of data w.r.t time. One of my colleague (Muhammad Yasrab) gave me this py code:

import xarray as xr

Load the NetCDF file

file_path = ‘/.nc’ # Change this to your file path
output_path = ‘/.nc’ # Path for the renamed output

Open the NetCDF file

ds = xr.open_dataset(file_path)

Check if ‘valid_time’ exists and rename it

if ‘valid_time’ in ds:
ds = ds.rename({‘valid_time’: ‘time’})
else:
print(“‘valid_time’ variable not found.”)

Save the modified dataset to a new NetCDF file

ds.to_netcdf(output_path)

Close the dataset to free resources

ds.close()
print(f"File saved as {output_path}")

This does convert the valid_time to time without loss of data. I am still validating the results which I got with this data. Apparently, they look fine. You can give it a try.

3

Hi,

Thanks for the answer. I could change the valid_time into time.

I still have a problem to concatenate files with cdo mergetime as valid_time is still in the dimensions and time has not the correct attribute UNLIMITED : I have
dimensions:
valid_time = UNLIMITED ; // (0 currently)
time = 12 ;
longitude = 1440 ;
latitude = 721 ;

How can I remove valid_time from the dimensions et get time = UNLIMITED ; // (12 currently) ?
Thanks

4

I use NCO, but I am sure you can find the appropriate alternative. You can try following:
module load NCO/5.1.3
make time variable dimensionless as you might get error while attempting to concatenate (ncrcat: ERROR no variables fit criteria for processing) --mk_rec_dmn time filename.nc outputfilename.nc (for all required files)
then concatenate using ncrcat -h

In my case, end result was:
dimensions:
latitude = 721 ;
longitude = 1440 ;
time = UNLIMITED ; // (8760 currently)

I have used files after this process in my model and they are running fine.

Hope it helps.

5

Hi,

Thanks for the answer.

Which command do you use with the following attributes (ncrcat ?)
–mk_rec_dmn time filename.nc outputfilename.nc.

Best regards,

6

Hello

You can use:
ncks --mk_rec_dmn time in.nc out.nc
makes the dimension “time” the record dimension

(reference: NetCDF operators (NCOs) for file manipulation and simple
calculations Para (9) Fixing the time variable, Part I: Adding a record dimension to a file)

7

Hi,

Thanks a lot for your help and for the references.
I could update my files.

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