[CF-metadata] Standardizing how ensemble (realization) axes are encoded

From: Jonathan Gregory <j.m.gregory>
Date: Fri, 15 Nov 2013 17:09:04 +0000

Dear all

This is partly a reply to various off-list emails.

I don't believe that the current CF standard says anything specifically about
ensemble axes. We did discuss introducing axis="E" but that wasn't adopted. The
axis attribute is generally redundant (the same came be deduced from mandatory
units, positive att or standard_name). I think it would be better to use the
standard_name to indicate an ensemble axis, whether collapsed or not.

Jamies Kettleborough has reminded us that we introduced the standard_name of
realization for ensemble members. (I did have a memory of that, but I searched
the table for a spelling with S rather than Z!) So I withdraw my suggestion of
new standard names for this. I think that the existing convention permits a
cell_methods entry of "realization: METHOD", when there is no dimension named
"realization", to indicate that an ensemble axis has been collapsed using
the METHOD stated. In the case where a cell_methods entry gives a name that is
not a dimension name, it's interpreted as a standard name, and it means "over
all available values".

Cheers

Jonathan
Received on Fri Nov 15 2013 - 10:09:04 GMT