CDO

Dear Zeinab Salah,

1. eca_pd expects a time series of daily precipitation sum. For your file, it seems to be reasonable to average these time steps and multiply with 8. One requirement for that is that these 8 timesteps cover one day.
2. Unfortunately, the date of highest one day precipitation is not saved with its value in the output file when using eca_rx1day. I am revising all climate index operators and will try to change that behavior.
There is also the operator eca_rx5day for highest 5 day amount however since you are free to provide infiles with a different frequency than daily precipitation amount, you can also use the eca_rx1day operator for other than highest one day precipitation. Just apply runsum over your input time series of precipitation amount with the running window of interest and specify it as input for eca_rx1day.

Best regards,
Fabi

Dear Fabi,
Thank you for your fast response.
my file contains mean of precipitation flux in kg/m2/s every 3 hours, so what I do is:
cdo daysum infile.nc daysum_file.nc
and to convert it to mm/day
cdo mulc,3600 daysum_file.nc daysum_file2.nc
cdo eca_pd daysum_file2.nc out.nc
Are these steps right?

Instead of

cdo daysum infile.nc daysum_file.nc
cdo mulc,3600 daysum_file.nc daysum_file2.nc
cdo eca_pd daysum_file2.nc out.nc

you could also pipe these operators in order to save I/O and you have to add mulc,3:

cdo eca_pd -mulc,3600 -daysum -mulc,3 infile.nc out.nc

mulc,3 is necessary since you have 3 hourly averages but you would like to have the three hour sum. I am sorry, I misunderstood that in the first place as well.
Please check that the time stamp of the records are inside the three hours average interval (cdo info gives you time information). So if the value covers the average from 00:00-03:00, the time stamp should be 01:30. Otherwise, if the time stamp is at the end of that interval, the value for 00:00 may be processed for the wrong day.

Best regards,
Fabi

thanks Fabi,
you are right, I miss to multiply 3.
the value of 00:00 includes in the next day, not in the same day.
how can I sum the values of hours : 03,06,09,12,15,21,00, every day?
best regards,
Zeinab

I tried to use timselsum to sum every 8 timesteps
cdo timselsum,8,0,8 infile.nc outfile.nc
is it right?

Best regards,
Zeinab

You could include shifftime to set the correct time values and then proceed with daysum:

cdo eca_pd -mulc,3600 -daysum -mulc,3 -shifttime,-90m infile.nc out.nc

Thanks a lot Fabian, it works

Hello Zeinab and Fabian,
Please correct me if wrong- you would need to multiply with 86400 rather 3600- isn't it? I am working with a NetCDF file that comes with 3 hours precipitation data with units kg/m2/sec. Likewise Zeinab, I also need to convert this into mm/day. Here is what I am doing- let me know if I am missing something.

cdo daysum infile.nc Daily_out.nc
cdo mulc,86400 Daily_out.nc OutIn_mmday.nc

Dear Ameer,
My file comes with average 3 hours precipitation data with units kg/m2/sec, as your file, therefore, Fabian told me to multiple with 3 to calculate summation (not average) of precipitation during every 3 hours, and then make daysum to collect all precipitation during the day. When you multiply this value with 3600, you convert it to mm, because you already collect all precipitation during 24 hours.
Hope this help you.