Dear Dirk > For sea_ice_extent, there is currently no definition in the CF > convention. This variable is somewhat odd in a CF context, as it only > makes sense when applied over several grid cells. > > Hence, we suggest to adopt a definition which implies usage over several > grid cells: > > sea_ice_extent: Total area of all grid cells that are covered by a > minimum of a given area fraction [usually 15 %) of sea ice in a > specified region".
I agree that it needs a definition. It is like sea ice area (m2) in being an extensive quantity which is integrated over the area considered, but I agree that extent is not meaningful unless there is some discretisation of area. I would suggest that we could allow for the possibility of the threshold being other than 15%, following practice for other standard names (as in recent emails of Martin's), like this sea_ice_extent: Total area of all grid cells in which the sea ice area fraction equals or exceeds a threshold. By default the threshold is 15%. The threshold can be specified by supplying a coordinate variable or scalar coordinate variable with standard_name of sea_ice_area_fraction. Would something like that be OK? Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
