Dear Mark I wonder what you think about this (from an email I sent on Fri, but it seems that it might not have got posted until yesterday):
> 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? I've thought a bit more about this. Since there is only *one* member from the original ensemble (rather than a subset of more than one) could we not regard this as a collapse by a point cell_method? The point method represents variation within the uncollapsed dimension by selecting the value at a particular location. That is exactly what you are doing by selecting one member from the ensemble. If it were a cell_method, then as discussed in ticket 108, we could record the original ensemble size as the original dimension e.g. cell_methods="realization: point (dimension: ensemble)" where realization is an existing standard name, and ensemble is a netCDF dimension containing the original ensemble size. No standard name would be needed. 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 ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
