Here I'm going to describe how to work with CDO if you work with CMIP5 climatic data
The intention with this info (and scripts) is to provide a basic understanding of how you can use CDO to speed-up your netCDF file data manipulation.
More info go directly to the Max Planck Institute CDO website
If you work on a MacOS Platform this guide is for you. For others operative systems go to:
Please contact Isaac Brito-Morales if you want to use these scripts, or to provide feed-back.
I couldn't install CDO from homebrew so I followed the instruction and downloaded MacPorts. MacPorts is an open-source community initiative to design an easy-to-use system for compiling, installing, and upgrading the command-line on the Mac operating system.
After the installation (if you have admin rights) open the terminal and type:
port install cdo
If you don't have admin rights, open the terminal and type:
sudo port install cdo and write your password
Browsing and browsing, I found a quick visual browser that allows you to explore netCDF files very easily: ncview
To install ncview, open the terminal and type:
port install ncview
To use ncview open the terminal and type:
cd ~/download/data/ (where my netCDF file is located).
Check if your file is there with
ls -lthr
and then type ncview EN.4.2.1.f.analysis.g10.196001.nc to use ncview
See the Github repo to access all files.
If you want to regrid and interpolate a netCDF file with CDO, the easiest way (for me) is create a standard grid with the argument griddes.
Using the EN.4.2.1.f.analysis.g10.196001.nc (which has a 1º of spatial resolution) I will create a standard of 1ºx 1º. In the terminal type:
cdo griddes EN.4.2.1.f.analysis.g10.196001.nc > EN4_grid.gr
Now you have a new file in your directory called EN4_grid.gr. Type vi EN4_grid.gr in the terminal to explore your new grid.
To regrid a netCDF file using CDO you will have to use the argument remapbil, which is the stands for bilinear interpolation. In the terminal type:
cdo remapbil,EN4_grid.gr, EN.4.2.1.f.analysis.g10.196001.nc EN.4.2.1.f.analysis.g10.196001_regrid.nc
With the first part of the code (cdo remapbil,EN4_grid.gr,) you are telling CDO to remap your input file using a a bilinear interpolation based on a standard grid file (previous EN4_grid.gr). The second part is your input file that you want to regrid (EN.4.2.1.f.analysis.g10.196001.nc) and your new regrided file (or output file = EN.4.2.1.f.analysis.g10.196001_regrid.nc)
NOTE: In this example I'm regridding the same file, but you can repit the same process for any input file
The previous "regridding process" works fine if you have one or two netCDF files. However, if you have multiple netCDF files (which is the most cases of CMIP5 climatic models) the best way to do it is to write a simple shell script to iterate the same process for every file.
Look the components of the shell file cdo_rg.sh from the Github repo
If you have problems to run the script open the terminal and type:
chmod +x cdo_rg.sh
cdo yearmean calculates the annual mean of a monthly data input netCDF file
cdo yearmin calculates the annual min of a monthly data input netCDF file
cdo yearmax calculates the annual max of a monthly data input netCDF file
cdo mergetime [in progress]
NOTE: you can repeat the same process described above for multiple files. See the Github repo to access the scripts.