Changes between Version 13 and Version 31 of Ticket #142


Ignore:
Timestamp:
01/04/16 06:16:30 (4 years ago)
Author:
markh
Comment:

I have updated this proposal to take account of source and institution information for model multiplicity definition.

I have also added a short section on ensemble labelling, including a proposed new standard name: ensemble_member_label, canonical unit (a string value is expected) for providing string labels for ensemble members.

I remain worried by the approach under discussion for identifying original ensemble size using cell methods. I think that this information, in the context of my use case, is information about the coordinate variable, not the data variable.

Given the lack of agreement on this topic, I have removed it completely from this proposal. It is an additive change, which ever route is adopted. I propose we evaluate this ticket without that detail; we can return to it later if the rest of this proposal is deemed suitable.

Does this updated proposal have sufficient merit that it may be adopted? Are there remaining areas of concern?

thank you

markh

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  • Ticket #142 – Description

    v13 v31  
    1919    ==== 4.6 Ensemble Coordinate ====
    2020
    21     Variables representing an ensemble or collection of realizations shall have an attribute `axis` with a value `E`.  These variables are discrete, as described in section 4.5.  They do not represent continuous quantities.
     21    Variables representing an ensemble or collection of realizations shall have an attribute `axis` with a value `E`.  These variables are discrete, as described in section 4.5;  they do not represent continuous quantities.
    2222
    23     Ensemble variables have a number of optional standardised attributes available for use.  Further bespoke attributes to describe the ensemble in project specific ways are allowed.
     23    Ensemble variables have a number of optional standardised attributes available for use.  Further bespoke attributes to describe the ensemble in project specific ways are always allowed.
    2424
    25     ===== 4.6.1 Ensemble Size =====
     25    ===== 4.6.1 Identifying Members =====
    2626
    27     An ensemble coordinate may include an attribute named `ensemble_size` representing the original size of the ensemble.
     27    A data variable representing an ensemble will commonly have an ensemble coordinate with the standard name `realization`; this is not mandatory. The `realization` standard name is used to provide a unique identifying number to each ensemble member within the ensemble.
    2828
    29     This attribute shall have a value which is a positive integer.
     29    An ensemble coordinate providing a string label for each ensemble member within the ensemble may also be included.  The standard name `ensemble_member_label` is proposed (canonical unit = '' (string expected)); this name is not yet approved as a standard_name.  An `ensemble_member_label` shall have unique values and missing values are not allowed.
    3030
    31     This value provides a context for the realization, which is preserved though sub-setting, slicing and statistical processing.  it is expected to remain unchanged through such operations on the data variable, which will alter the values of the realization coordinate.
     31    ===== 4.6.2  Ensemble Control Member ====
    3232
    33     ===== 4.6.2 Single Model Ensemble  =====
    34 
    35     An ensemble coordinate may include an attribute named `single_model_ensemble` representing the assertion that the ensemble of members all originate from the same numerical model.
    36 
    37     This is a boolean field and may only contain the values `true` or `false`.
    38 
    39     The absence of this attribute shall not be interpreted as a positive or negative statement.  No inference on the models providing ensemble members shall be inferred from the absence of this attribute.
    40 
    41     ==== 4.6.3 Ensemble Control Member ====
    42 
    43     An ensemble coordinate may include an attribute named `ensemble_control_member`.
     33    An ensemble coordinate with the standard name `realization` or `ensemble_member_label` may include an attribute named `ensemble_control_member`.
    4434
    4535    This value provides a definition that one member of the ensemble is the control member and identifies this member.  This control member shall have the identified value within the ensemble coordinate's data.
     
    4737    The absence of this attribute shall be interpreted as a negative statement, explicitly stating that there is no control member identified within the ensemble.
    4838
     39    ==== 4.6.3 Single or Multiple Model Ensemble  =====
     40
     41    An ensemble coordinate may be identified as being from one model or multiple models by providing further variables identified as coordinates or auxiliary coordinates by the data variable.  All of these coordinates shall have an attribute `axis` with a value `E`.
     42
     43    The standard name's `source` and `institution` are used to identify the multiplicity of models which the ensemble is taken from, one other or both may be present.
     44
     45    Such coordinates may be scalar coordinate variables or they may be attached to the same dimension(s) as other ensemble coordinates referenced by a data variable.  Scalar coordinates are commonly used to define a single model ensemble; in this case, this is informationally equivalent to auxiliary coordinates with identical values.
     46
     47    The absence of such `source` and `institution` coordinates shall not be interpreted as a positive or negative statement.  No inference on the multiplicity of models which the ensemble is taken from shall be inferred from the absence of such coordinates.
     48
     49
     50
    4951== 5. Benefits ==
    5052
    5153    Information regarding the nature of an ensemble is encoded in an ensemble coordinate, analogous to temporal coordinates.
    5254
    53     Encoding of the ensemble size, the presence of a control member and the single or multiple model nature of the ensemble is standardised.
     55    Encoding of the presence of a control member and the single or multiple model nature of the ensemble is standardised.
    5456
    5557    Future standardisation of ensemble characteristics has a model to follow.