Dear João,
glad to see that the problem with plotting the data in IDL has been solved.
From the CM SAF Training Team we are supporting the use of the climate data operators (cdo) and R for analysing and visualising the CM SAF data.
In case you are flexible on the software you want to use for data analysis you might want to have a look at the 'Introduction to the Software Tools' Section and check out the CM SAF Toolbox and its Instructions. You will find software scripts based on these free software tools to calculate and display multi-annual monthly averages of the CM SAF data, which you might find helpful for your application.
Kind regards,
Jörg