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:[email protected]] *On
Behalf Of *Karl Taylor
*Sent:* 07 November 2014 00:39
*To:* [email protected]
*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 [[email protected]
<mailto:[email protected]>] on behalf of Jonathan Gregory
[[email protected] <mailto:[email protected]>]
Sent: 31 October 2014 15:25
To:[email protected] <mailto:[email protected]>
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"<[email protected]>
<mailto:[email protected]> -----
Date: Fri, 31 Oct 2014 14:50:53 +0000
From: "Hedley, Mark"<[email protected]>
<mailto:[email protected]>
To: John Graybeal<[email protected]>
<mailto:[email protected]>
CC: CF Metadata List<[email protected]>
<mailto:[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]
<mailto:[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]><mailto:[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]><mailto:[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]><mailto:[email protected]>
<mailto:[email protected]>] on behalf of Jonathan Gregory [[email protected]
<mailto:[email protected]><mailto:[email protected]>
<mailto:[email protected]>]
Sent: 30 October 2014 16:40
To:[email protected]
<mailto:[email protected]><mailto:[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]><mailto:[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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