Thank you for your answer.
You are right, nco commands are sometimes a good choice to perform calculations.
But the example I have detailled is a very simple case of more complicated calculs where all the
nested variable definitions offered by ferret and its grammar is very well adapted.
It means opening multiple files, combining variables with different conditionnal definitions, producing
a plot with a same concise code.
I think it would be quite a big job to translate those ferret scripts with nco commands,
even with the ncap2 command that it is powerfull. So I would like to stay with ferret processing
in my case and get a solution to handle processings for "large" time series.
Data Analysis and Visualization Engineer
LSCE/IPSL, CEA-CNRS-UVSQ laboratory
LSCE - Climate and Environment Sciences Laboratory
IPSL - Institut Pierre Simon Laplace