I support the idea that the term "ensemble" be allowed (by whatever
machinery) as an alias for "realization". Two reasons
1. the fact that 3 out of 3 of us failed to find "realization" until
Jamie reminded us, is a data point on what less informed CF users
will experience when they search the users guide
2. compatibility with CDM
axis="E" also seems like an appropriate step to maintain consistency
with other well known axis types, given the high likelihood that
ensemble axes will become commonplace in the future.
- Steve
On 11/15/2013 9:43 AM, Kettleborough, Jamie wrote:
Hello,
In the original proposal for an ensemble like axis we used the standard_name
'realization' because it included things that weren't obviously model ensembles
- they may be forecasts or projections generated by statistical methods - but
that could be handled in a way similar to model ensembles. The paper:
http://www.climateprediction.net/wp-content/publications/nature_allen_051000.pdf
is an example of this sort of technique.
The use of 'realization' has been questioned before on this list - so I'd be
very happy to review its use. If 'ensemble' is more familiar and useful then
that would be fine. (I think this can be handled with aliases - is that right?)
I think there is a complication with ensemble based statistics (sorry I haven't
followed this latest thread close enough to know whether it has been talked
about). You often weight each ensemble memember e.g. based on some estimate of
that ensemble member's likelihood - before calculating the ensemble statistic.
I think there is a thread somewhere like
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2007/046103.html which
discussed this previously.
Now apologies: in my usual useless style on this list - I probably won't manage
to follow this up in any detail - but since Jonathan mentioned me I thought I
needed to try to fill in some background.
Jamie
-----Original Message-----
From: Jonathan Gregory [mailto:[email protected]]
Sent: 15 November 2013 17:09
To: [email protected]
Cc: [email protected]; Steve Hankin; Kettleborough,
Jamie; Hedley, Mark
Subject: [CF-metadata] Standardizing how ensemble
(realization) axes are encoded
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
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