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" <[email protected]> ----- > Date: Fri, 31 Oct 2014 14:50:53 +0000 > From: "Hedley, Mark" <[email protected]> > To: John Graybeal <[email protected]> > CC: CF Metadata List <[email protected]> > 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 [[email protected]] > 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 > <[email protected]<mailto:[email protected]>> 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 > [[email protected]<mailto:[email protected]>] > 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 > [[email protected]<mailto:[email protected]>] > on behalf of Jonathan Gregory > [[email protected]<mailto:[email protected]>] > Sent: 30 October 2014 16:40 > To: [email protected]<mailto:[email protected]> > 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 > _______________________________________________ > CF-metadata mailing list > [email protected]<mailto:[email protected]> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > On Oct 30, 2014, at 01:40, Hedley, Mark > <[email protected]<mailto:[email protected]>> 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 > _______________________________________________ > CF-metadata mailing list > [email protected]<mailto:[email protected]> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > _______________________________________________ > CF-metadata mailing list > [email protected]<mailto:[email protected]> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
