[CF-metadata] original_ensemble_size

Karl Taylor taylor13 at llnl.gov
Wed Jul 22 15:53:14 MDT 2015


Hi all,

I'm still curious about something:

Suppose we have the temperature field stored from one member of an 
ensemble of size 10.   We want to make the size of the ensemble known to 
the user.   We store 10 as a scalar variable with standard name 
"ensemble_size", but how does that scalar get associated with our 
temperature variable (other than it having being stored in the same file)?

cheers,
Karl

On 7/22/15 1:59 AM, Hedley, Mark wrote:
> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> CF-metadata mailing list
>>>>> CF-metadata at cgd.ucar.edu
>>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>>
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>>
>

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