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
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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
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_______________________________________________
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