Collection of CMIP7 REF recipes

[axel-lauer]

Collection of CMIP7 REF recipes

This issue is intended as an overview on recipes to be used for CMIP7 REF (rapid evaluation framework). The following recipes have been implemented so far:

• seasonal cycle of the NH sea ice extent (requires ESMValCore update https://github.com/ESMValGroup/ESMValCore/tree/fix_siextent): https://github.com/ESMValGroup/ESMValTool/blob/ref_sea_ice_extent/esmvaltool/recipes/ref/recipe_ref_siextent_seasonal.yml