Changes between Version 31 and Version 37 of Ticket #142


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Timestamp:
01/15/16 02:10:23 (4 years ago)
Author:
markh
Comment:

New Content

Conventions

4.6 Ensemble Coordinate

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.

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.

4.6.1 Identifying Members

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.

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.

4.6.2 Ensemble Control Member ====

An ensemble coordinate with the standard name realization or ensemble_member_label may include an attribute named ensemble_control_member.

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.

The absence of this attribute shall be interpreted as a negative statement, explicitly stating that there is no control member identified within the ensemble.

4.6.3 Single or Multiple Model Ensemble =

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.

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.

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.

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.

Appendix A

| ensemble_control_member | D | C | ref:<<ensemble-coordinate>> | The identifier of the member of the ensemble which is the control member. |

Conformance Document

4 Coordinate Types

Requirements:
  • The axis attribute may only be attached to a coordinate variable or auxiliary coordinate variable only.
  • The only legal values of axis are X, Y, Z, and T and E (case insensitive).
  • The axis attribute must be consistent with the coordinate type deduced from units and positive.
  • The axis attribute is not allowed for auxiliary coordinate variables.
  • A data variable must not have more than one coordinate variable with a particular value of the axis attribute.
4.6.2 Ensemble Control Member ====
Requirements
  • A variable may have an attribute ensemble_control_member only if it has an axis attribute of E and a standard_name of either realization or ensemble_member_label.

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  • Ticket #142 – Description

    v31 v37  
    4747    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.
    4848
     49    ==== Appendix A ====
     50
     51    | **`ensemble_control_member`** | D | C | ref:<<ensemble-coordinate>> | The identifier of the member of the ensemble which is the control member. |
     52
     53
     54    ==== Conformance Document ====
     55
     56
     57    ==== 4 Coordinate Types ====
     58
     59    ===== Requirements: =====
     60
     61    * The axis attribute may ~~only~~ be attached to a coordinate variable '''or auxiliary coordinate variable only'''.
     62    * The only legal values of axis are X, Y, Z, ~~and~~ T''' and E''' (case insensitive).
     63    * The axis attribute must be consistent with the coordinate type deduced from units and positive.
     64    * ~~The axis attribute is not allowed for auxiliary coordinate variables.~~
     65    * ~~A data variable must not have more than one coordinate variable with a particular value of the axis attribute.~~
     66
     67
     68    ===== 4.6.2  Ensemble Control Member ====
     69
     70    ===== Requirements =====
     71
     72    * A variable may have an attribute `ensemble_control_member` only if it has an `axis` attribute of `E` and a standard_name of either `realization` or `ensemble_member_label`.
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