Hello,
Is it worth introducing the new standard name 'ensemble' which is an alias for 'realization'? (Have we talked about this before?)
Initially we used 'realization' to try to be more general than model studies (i.e. samples from distributions produced by statistical techniques) but
1. I'm not sure there has been much exchange of non-model data using 'realization' (please correct me if I'm wrong)
2. The term 'realization' has caused confusion
Jamie
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Karl Taylor
Sent: 07 November 2014 00:39
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] realization | x of n
Dear Mark and all,
I think it be clearer to a broader community and more general to define:
standard_name = ensemble_size
description: The number of members constituting an ensemble.
This would be more generic than mentioning "forecasting", since the size of an ensemble of climate simulations (which are not necessarily "forecasts") might also be of interest and worth recording.
best regards,
Karl
On 11/6/14, 3:51 AM, Hedley, Mark wrote:
I suppose you could attach this information to the data variable using a scalar coordinate variable - is that what you think?
yes, that seems suitable to me
mark
________________________________________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu<mailto:cf-metadata-bounces at cgd.ucar.edu>] on behalf of Jonathan Gregory [j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>]
Sent: 31 October 2014 15:25
To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>
Subject: [CF-metadata] realization | x of n
Dear Mark
Thanks for clarifying the use-case. I agree that we don't have an existing way
to provide this information, and it would be fine to give it a new standard
name. I suppose you could attach this information to the data variable using a
scalar coordinate variable - is that what you think?
Best wishes
Jonathan
----- Forwarded message from "Hedley, Mark" <mark.hedley at metoffice.gov.uk><mailto:mark.hedley at metoffice.gov.uk> -----
Date: Fri, 31 Oct 2014 14:50:53 +0000
From: "Hedley, Mark" <mark.hedley at metoffice.gov.uk><mailto:mark.hedley at metoffice.gov.uk>
To: John Graybeal <jbgraybeal at mindspring.com><mailto:jbgraybeal at mindspring.com>
CC: CF Metadata List <cf-metadata at cgd.ucar.edu><mailto:cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] realization | x of n
I'm happy to be more specific and stick with
'original ensemble'
as it meets my use cases just fine.
So, I think that the proposal stands as:
standard_name:
number of realizations
units:
''
description:
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).
many thanks
mark
________________________________
From: John Graybeal [jbgraybeal at mindspring.com<mailto:jbgraybeal at mindspring.com>]
Sent: 30 October 2014 23:14
To: Hedley, Mark
Cc: CF Metadata List
Subject: Re: [CF-metadata] realization | x of n
Glad you liked the text!
Regarding 'given ensemble' vs 'original ensemble', how can we resolve the ambiguity? That is, if you use this attribute, how will the user know what ensemble the attribute is in reference to?
If the 'common practice among forecasters' (and required capability) is exclusively describing the originating ensemble, I propose the name and text should reflect that narrower definition, to avoid misuse. (I'm hoping for this case.)
If the common practice includes both use cases, somehow the user needs to derive which meaning applies -- either we need to define two standard names, or suggest in the definition that the variable name or long_name should resolve it, or something. (We could be deliberately vague as well, but a sentence like "This could refer to either the original ensemble for this realization, or a more recent collection in which the realization occurs." would help make that explicit.)
John
On Oct 30, 2014, at 10:44, Hedley, Mark <mark.hedley at metoffice.gov.uk<mailto:mark.hedley at metoffice.gov.uk><mailto:mark.hedley at metoffice.gov.uk><mailto:mark.hedley at metoffice.gov.uk>> wrote:
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<mailto:jbgraybeal at mindspring.com><mailto:jbgraybeal at mindspring.com><mailto: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<mailto:cf-metadata-bounces at cgd.ucar.edu><mailto:cf-metadata-bounces at cgd.ucar.edu><mailto:cf-metadata-bounces at cgd.ucar.edu>] on behalf of Jonathan Gregory [j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk><mailto:j.m.gregory at reading.ac.uk><mailto:j.m.gregory at reading.ac.uk>]
Sent: 30 October 2014 16:40
To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu><mailto:cf-metadata at cgd.ucar.edu><mailto: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><mailto: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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