BUG: change of internal and external climatology

Bug

Error description

When calculating the climatological skill score, the data sets are interchanged for accident. Clearification:

internal means that the data is already known to the model -> train and val

external means that the data is not known to the model and a good skill score would be harder to archive (but also will reward a forecast more= -> test

Error message

silent error

First guess on error origin

Error origin

Solution

• use train_val set as internal climatology
• use test set as external climatology
• update required in any description?
• confirm also that skill scores are calculated on test data