"ydaysub" in daily anomalies for a year

Hi,
I'm not expert in climate but I want to obtain daily anomalies for one specific year (2017) from 30-year long period (1981-2010). In other words, anomalies for each day of 2017 year which comes from the difference between daily values reported in 2017 and mean values of 1981-2010 period.

I'm working with two datasets from ERA5 land hourly, after some modifications both are expressed in daily values:

t2m_daily_2017.nc
t2m_daily_1981-2010.nc

Looking some posts in this forum and the CDO documentation, I found the ydaysub operator and tried to replicate:
cdo ydaysub t2m_daily_2017.nc -ydaymean t2m_daily_1981-2010.nc daily-anomaly_2017.nc

I'd like to know this is right code or not, and how it can be improved/changed.

Thanks in advance
Brian

Replies (3)

RE: "ydaysub" in daily anomalies for a year - Added by Ralf Mueller almost 3 years ago

hi Brian!

cdo ydaysub t2m_daily_2017.nc -ydaymean t2m_daily_1981-2010.nc daily-anomaly_2017.nc looks good to me.

if you want to get more familiar with these operators it might help to play around with them using artificial time series data. I often use something like this

cdo -infov -settaxis,2001-01-01,12:00:00,1days -expr,'seq=seq/seq' -seq,1,365 t.nc

as a basis. It creates a one-year time series of daily values of 1.0. you can adapt the time unit 1days to the operators you are interested in and the part with -expr,'seq=seq/seq' can be extended to create special values which will ease the verification of what operators like yhoursum or ydaymean do in your application.

hth
ralf

RE: "ydaysub" in daily anomalies for a year - Added by Brian Yalle almost 3 years ago

Thanks Ralf for your answer!

RE: "ydaysub" in daily anomalies for a year - Added by Brian Yalle almost 3 years ago

If I just want to obtain the mean daily values for an entire year considering the 30-year period (1981-2010), the code would be like:
cdo ydaymean t2m_daily_1981-2010.nc t2m_daily_mean_30year.nc?

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