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: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
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