[CF-metadata] CMIP6 Sea Ice MIP: Integrated quantities

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 21 Jul 2016 13:53:56 +0100

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
Received on Thu Jul 21 2016 - 06:53:56 BST