The ERA5 dataset is too large to CMORize and then store, e.g. one year of a single hourly variable takes up 34 GB after CMORization. Instead ESMValCore should be able to find ERA5 data already available (either on a cluster or downloaded through era5cli) and CMORize while reading it using fixes.

This can also be used as an example of how to add support for analyzing model data in native format, e.g. EMAC data.