Extension to external_variables Syntax for Masks and Area Fractions
|Reported by:||martin.juckes||Owned by:||cf-conventions@…|
Description (last modified by martin.juckes)
Ticket #145, now accepted, proposes a new attribute, external_variables, to indicate when a variable referred to in the cell_measures attributes is in another file. This ticket relates to masks and area fractions used in the cell_methods attribute which may be associated with another variable. For instance, if we have cell_methods = area: mean where sea_ice and, in another file, a variable siconc which contains the sea ice area fraction. At present, there is no way within the convention to indicate, in the file containing the cell_methods statement, that the variable siconc is supplied separately. In earlier CMIP archives it was reasonably easy to determine when a mask or area fraction was available for a particular cell methods operation. For CMIP6 this is not so easy, as there are a substantial number of area fraction arrays covereing different aspects of the cryosphere and land surface.
The proposal is to allow the external_variables attribute to include terms of the form sea_ice:siconc to indicate that an area_type has an associated variable in an external file.