[CF-metadata] original_ensemble_size

Hedley, Mark mark.hedley at metoffice.gov.uk
Wed Jul 22 02:59:08 MDT 2015


Hello John, Karl et al

I'm not sure I agree with John's last statement. I think that an ensemble is a defined collection of members, so my need is the need for ensemble size to be defined explicitly.
The distinction that not all members may be present characterises the need for this metadata descriptor, rather than just using the dimension size of realization, which does not meet my requirement.

On reflection, I think that I prefer Karl's name of 'ensemble_size'

To restate my use case, I have a data set from an ensemble, where there is a coordinate variable called 'realization'.  Let's say there are 23 members, this dimension is size 23.

I want to reference the number of members in the ensemble, whilst sub-setting the data variable in various ways.

The suggestion is to add a scalar coordinate to my original dataset, which contains the number of members in the ensemble.  Then any sub-setting operation will retain this coordinate, and I will always be able to state that this member is member 0 of 23, 5 of 23 etc

One requirement I have is to slice this variable, to result in a 2D data array, 2 1D coordinate variables: latitude and longitude; with all other coordinates as scalars.

If it is reasonable to talk about an ensemble as a defined collection of members, then I agree with Karl, that a standard_name of 'ensemble_size' fits the bill.  The description fits my use case nicely

many thanks
mark


________________________________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of John Graybeal [jbgraybeal at mindspring.com]
Sent: 22 July 2015 05:52
To: Karl Taylor
Cc: CF Metadata List
Subject: Re: [CF-metadata] original_ensemble_size

Karl,

To my understanding (then and now), the use case is explicitly not what your definition describes. The entire point of the request was to provide a label that was clearly distinguished from the typical concept of ensemble size.

John



On Jul 21, 2015, at 16:36, Karl Taylor <taylor13 at llnl.gov<mailto:taylor13 at llnl.gov>> wrote:

Dear all,

I wonder if the following might also meet requirements of the use case:

name: ensemble_size

description: The number of member realizations in an ensemble.  This name provides context for any specific realization, which might not be co-located with the other members of the ensemble.

Karl

On 7/20/15 9:49 PM, John Graybeal wrote:
To save others the lookup, the use case phrasing that Mark signed on to were these words: "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."  The entire thread is titled 'realization | x of n', but it is pretty, umm, rich with detail.

The last email before discussion went silent appears to be mine:

Modified to fit Mark's use case, I think suitable text is:

name: original_ensemble_size

description: The number of member realizations in the originally constituted 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).

This does not mention forecasting, preserves the origination concept, and gives a bit of context, without constraining the application. It could even be an ensemble of observations, or cat videos, or ... you get the idea.

I will let someone else provide the example of how that is associated with the variable, it will be more authoritative!

John


On Jul 20, 2015, at 14:42, Karl Taylor <taylor13 at llnl.gov<mailto:taylor13 at llnl.gov>> wrote:

Hi Mark,

I didn't quite understand how the standard name gets associated with a variable (containing 1 or more realizations from the ensemble).   Someone said it was through a scalar coordinate variable, but I don't see how the ensemble member is a function of the ensemble size, so why would this be appropriate?

Could you supply an example?

Also, I didn't follow why "original" was included in "original ensemble size".  Surely, you wouldn't report this number unless you thought the ensemble size was pretty much set and wouldn't change.  In that case there shouldn't be a need for a "modified ensemble size", so wouldn't "ensemble size" suffice?

thanks,
Karl


On 7/20/15 9:24 AM, Hedley, Mark wrote:
Hello CF

Late last year we had a discussion about storing

original_ensemble_size

in a CF file
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2014/thread.html#57756

There were a few options discussed, with John Graybeal making the suggestion

original_ensemble_size
description: The number of members constituting an ensemble.


for a new standard_name definition, which seemed to fit the case very well

It does not seem to have been adopted into the standard names list as yet.

Please may this name and definition be adopted, or reasons not to detailed here?

thank you
mark





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