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:j.m.gregory at reading.ac.uk]
> Sent: 15 November 2013 17:09
> To: cf-metadata at cgd.ucar.edu
> Cc: caron at unidata.ucar.edu; 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
>
Received on Fri Nov 15 2013 - 10:43:40 GMT
