Thank you for the feeedback
John:
I like the text
In a model or operational forecast, the number of member realizations within a given ensemble. This provides context for any specific realization, for example orienting a member relative to its original group (even if the group is no longer intact).
I would like to use this as is in the proposal.
> Reviewing this and going back to your original request, there is still a likely point of confusion for users -- it isn't obvious that "given ensemble" refers not to the currently constituted collection, but to the one originally created with this realization.
> If you want that to be the use case for this standard_name (for everyone), I think 'within a given ensemble' needs to explicitly say something like 'within its originally created ensemble'. And perhaps the standard name itself should follow that thought, something like 'initial_number_of_realizations'.
I had thought about this, but my consideration was that there are ensembles which are created after the fact, not necessarily in the 'originally created' set; e.g. multi-model ensembles. I considered leaving the name so that it could be used in this context as well. This is not a strong use case for me, so I would be content to be more specific if that is preferred, but I didn't see the need to, so I left it more general. I'm happy to be guided on this aspect.
Jonathan:
> Maybe you are dealing with an intermediate case, having a subset of the ensemble members, and you want to record how many there originally were in total. Is this a common use case? It seems rather surprising to me. But I'm not sure that's what you mean.
Yes, this is what I mean. I have one of the ensemble members, I have chosen it from the collection and passed it to a friend, for reasons best known to myself; I want to label it as member x from emsemble of size y. I am confidently assured this is common practice amongst forecasters and the capability is required. It has been an explicit part of the GRIB specification for years.
>> seven of nine
> But this seems different. It's not the number of members there are, but the ordinal number (7) of this particular member. Why can't that be recorded in a variable with the existing standard_name of realization?
there are two pieces of information here, in CF terms this is:
realization = 7
number_of_realizations = 9
I just unpacked this into a single label, to illustrate the information wanted (but I seem to have reduced clarity again; never mind).
mark
________________________________
From: John Graybeal [jbgraybeal at mindspring.com]
Sent: 30 October 2014 17:10
To: Hedley, Mark
Cc: CF Metadata List
Subject: Re: [CF-metadata] FW: realization | x of n
Hi Mark,
It is a worry if the definition is a repetition or variant of the words in the name. In particular, the word 'realization' will be meaningful to modelers/forecasters but not universally.
My first desire was to generalize the term (e.g., 'how many entities are in a collection of that type of entity'), but I suspect that will be annoying to the primary users. So can we make it specific and say
In a model or operational forecast, the number of member realizations within a given ensemble. This provides context for any specific realization, for example orienting a member relative to its original group (even if the group is no longer intact).
Or else, define what we mean by 'realization' and 'ensemble'.
Reviewing this and going back to your original request, there is still a likely point of confusion for users -- it isn't obvious that "given ensemble" refers not to the currently constituted collection, but to the one originally created with this realization.
In my use case, the whole ensemble is not present, I only have a subset of the members. I have a metadata element telling me how many members there were at the time the ensemble was created, which I would like to encode.
If you want that to be the use case for this standard_name (for everyone), I think 'within a given ensemble' needs to explicitly say something like 'within its originally created ensemble'. And perhaps the standard name itself should follow that thought, something like 'initial_number_of_realizations'.
John
______________________________________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of Jonathan Gregory [j.m.gregory at reading.ac.uk]
Sent: 30 October 2014 16:40
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] FW: realization | x of n
Dear Mark
> Please may people raise any further concerns about a new standard name:
> number_of_realizations
> with a canonical unit of
> ''
> and a description of
> The number of member realizations within a given ensemble.
My concern is probably the same one as before. Sorry about that. Does this
mean the number of members the ensemble has got? If it does, why does it differ
from the ensemble dimension? If the ensemble dimension has been collapsed to
size 1, we could record this in cell_methods. Maybe you are dealing with an
intermediate case, having a subset of the ensemble members, and you want to
record how many there originally were in total. Is this a common use case?
It seems rather surprising to me. But I'm not sure that's what you mean.
> This name enables a single member from an ensemble to explicitly be labelled, e.g.
> seven_of_nine
> which is often required in operational forecasting.
But this seems different. It's not the number of members there are, but the
ordinal number (7) of this particular member. Why can't that be recorded in a
variable with the existing standard_name of realization?
Cheers
Jonathan
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On Oct 30, 2014, at 01:40, Hedley, Mark <mark.hedley at metoffice.gov.uk<mailto:mark.hedley at metoffice.gov.uk>> wrote:
Thank you for the discussion on the number of realizations in an ensemble.
Please may people raise any further concerns about a new standard name:
number_of_realizations
with a canonical unit of
''
and a description of
The number of member realizations within a given ensemble.
This name enables a single member from an ensemble to explicitly be labelled, e.g.
seven_of_nine
which is often required in operational forecasting.
I would like this to be added to the standard name list.
thank you
mark
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