Determination of anomalies for Geopotential height
Added by Abubakar Bello over 2 years ago
I want to calculate seasonal anomalies for geopotential height (JFM,OND and DJF). The DJF should span two different years.
Below is my approach and the years of interest are 1089,1996,2003 and 2015
Here are my steps for JFM
cdo yearmean -selmon,1,2,3 geo79-2020.nc 123yearmean.nc
cdo timmean 123yearmean.nc Tmean.nc
cdo -b 64 sub 123yearmean.nc Tmean.nc ano123.nc
To extract the years I did use
cdo selyear.2015 ano123.nc ano123.15.nc
cdo selyear.2003 ano123.nc ano123.03.nc
cdo selyear.1996 ano123.nc ano123.96.nc
cdo selyear.1989 ano123.nc ano123.89.nc
Are these steps the right way?
The outputs when plotted in Grads are off the grids
Replies (1)
RE: Determination of anomalies for Geopotential height - Added by doria avallone 4 days ago
This approach takes December from the previous year and January, February from the current year to calculate the DJF seasonal mean. Then it calculates the long-term mean and the anomalies similar to your approach for JFM.
Remember to adjust the filenames and paths according to your data structure and ensure that the years you’re interested in (e.g., 1989, not 1089) are correctly specified. If you continue to experience issues, it might be helpful to consult with a domain expert or further resources specific to CDO and GrADS. Keep in mind that my knowledge is based on information up to 2021, and you should verify these steps with the most current practices and data.
- Calculate DJF mean, considering December from the previous year
cdo -b 64 ymonmean -selmon,12 geo79-2020.nc DecPreviousYear.nc
cdo -b 64 ymonmean -selmon,1,2 geo79-2020.nc JanFebCurrentYear.nc
cdo -b 64 mergetime DecPreviousYear.nc JanFebCurrentYear.nc DJFmean.nc
- Calculate the long-term mean for DJF
cdo -b 64 timmean DJFmean.nc DJFTmean.nc
- Subtract the long-term mean from the DJF mean to get anomalies
cdo -b 64 sub DJFmean.nc DJFTmean.nc DJFano.nc
- Extract the years of interest
cdo selyear,2015 DJFano.nc DJFano15.nc
cdo selyear,2003 DJFano.nc DJFano03.nc
cdo selyear,1996 DJFano.nc DJFano96.nc
cdo selyear,1989 DJFano.nc DJFano89.nc