# Maintaining and Advancing the CF Standard for

#  Earth System Science Community Data

B.N. Lawrence[^1], R. Drach[^2], B.E. Eaton[^3], J. M. Gregory[^4], S.
C. Hankin[^5], R.K. Lowry[^6], R.K. Rew[^7], and K. E. Taylor^2^.

(please send comments to b.n.lawrence AT rl.ac.uk)

# Abstract

> The Climate and Forecast (CF) conventions governing metadata appearing
> in netCDF files are becoming ever more important to earth system
> science communities. This paper outlines proposals for the future of
> CF, based on discussions at an international meeting held at the
> British Atmospheric Data Centre in 2005. The proposal presented here
> is aimed at maintaining the scientific integrity of the CF
> conventions, while transitioning to a community governance structure
> (from the current situation where CF is maintained informally by the
> original authors).

## 1. Introduction

The Climate and Forecast (CF) metadata conventions are designed to
promote the processing and sharing of data stored in files created with
the netCDF API[^8]. Fundamental features of the conventions are that
CF-aware software can automatically determine the space-time location of
variables (facilitating analysis and graphical display), and metadata
describing each variable is sufficiently detailed to determine whether
variables from different sources are comparable. The general principles
of CF design are enumerated in Gregory (2003)[^9]:

1.  Data should be self-describing. No external tables are needed to
    interpret the file. For instance, CF encodings do not depend upon
    numeric codes (by contrast with GRIB).

2.  Conventions have been developed only for known issues. Instead of
    trying to foresee the future, features are added as required.

3.  The convention should be easy to use, both for data-writers and
    users of data.

4.  The metadata and the semantic meaning encoded through the metadata
    should be readable by humans as well as easily utilized by programs.

5.  Redundancy should be minimised as much as possible (so as to reduce
    the chance of errors of inconsistency when writing data).

CF was initiated in the climate modelling community because of the lack
of an adequate existing standard (although COARDS was a good basis, with
which CF remains backward compatible). CF is becoming the de facto
standard for storing outputs of atmospheric, ocean and climate models.
Interest may expand to related \"earth system\" communities, but few
users have thus far embraced the full self-descriptive capabilities
enabled by the CF-standard, perhaps because software that can interpret
all of this information has yet to be developed. Furthermore, \"standard
names\" have not yet been agreed on for certain quantities, and in some
cases the existing conventions are unsuitable or inefficient. To avoid
fragmentation of the potential user community, such issues must be
addressed more rapidly.

CF use is growing. As CF becomes more important to a diverse range of
communities, its boundaries of applicability are being stretched, and
the workload on the original authors is growing, such that it is not
possible to keep pace with requests for extensions. There have been
questions about how (and when) CF can evolve in the future, but it is
not possible to answer such questions with confidence given the current
situation where authorship of CF is a marginal activity on top of
already full workloads, with the authors' personal interests
representing only a part of the range of the user community. Moreover
the widespread use of CF means that its development must be undertaken
with great care and proper consultation.

This paper outlines some of the immediate issues that the CF community
is confronting, beginning with how CF transitions to community ownership
and maintenance. It is based on an extended discussion held at the
British Atmospheric Data Centre in June 2005 as part of the annual
Global Organisation for Earth System Science Portals (GO-ESSP) meeting.

## 2. CF Governance and Development

If CF is to become a widely accepted community standard, it is
imperative that the community (a) takes ownership of and responsibility
for the future trajectory of the standard and (b) invests substantial
resources in its development. To do this we need first a clear
definition of the boundaries of the problem (who are the CF community?)
and then to set in place a structure for governance and development
which:

-   Preserves the existing intellectual rigor,

-   Achieves rapid response to community requirements, and

-   Meets the needs of as much of the community as is possible.

In some circumstances these three "what" requirements will pull in
different directions. When this happens, one of the requirements of the
governance structure is to impose a set of constraints on CF evolution
that minimises this tension. To support the requirements we also need
agreement about three "how" issues:

-   How should CF maintenance be funded?

-   How should CF be maintained from a sociological perspective? (What
    organizational structures are needed?)

-   How should CF be maintained from a technological perspective? (What
    tools are needed?)

In this section we discuss the definition of "who is the CF community"
and these three "how" issues in regard to both what we believe is
achievable in the near term, and in terms of the three "what"
requirements.

### 2.1 Who is the CF Community?

Climate modellers initially dominated the CF community, but, recently
others (e.g., observational communities) have seized on CF as the
solution to their own format description problems. As these communities
have expressed their needs, new problems have arisen: for example,
different terminologies are used, Earth geometry is real, rather than
idealised, and standard names are needed for "raw" instrumental
measurements before they are converted to data which are independent of
the method of observation. Other problems can be anticipated,
particularly as interdisciplinary work progresses. The scope of CF
standard names, for example, will likely need to include observational
biological oceanography, atmospheric chemistry, forest-type
classification, etc.

Given that CF effectively consists of three sets of conventions -
vocabulary management, semantic concepts (axes, cells etc), and format
specific conventions (netCDF, for now), it is possible that different
communities may wish to be involved in different parts of the CF
evolution. For example, some users of CF are only interested in the CF
standard names, storing their data in other formats (HDF-EOS, NASA-Ames
etc), although this is problematic because some parameters need more
than just the standard names to be fully described (e.g. the cell
methods attribute describes the averaging); i.e., vocabulary and concept
are not entirely separated.

For CF to fulfil its mission as a medium of interchange for complex
information, the needs of users must be balanced with those of data
producers. In addition, the input from developers of software that can
interpret and use the CF metadata descriptions is vital. (It was noted
at the GO-ESSP meetings in both 2004 and 2005 that only a subset of
CF-defined metadata is interpretable and actually used by any real
software.) Furthermore, despite the name, forecasters have not been
greatly involved in developing CF.

The future of CF will inevitably involve use in earth system models, and
so the scope of CF will need to address the requirements of a wide range
of communities. Furthermore, CF does not exist in a vacuum. There are
other projects that are developing community standards for encoding data
and describing it: notably the Open Geospatial Consortium; the WMO
metadata initiatives; and controlled vocabularies in use in other parts
of the earth system science community. A significant challenge for the
CF community will be finding ways of interacting productively with these
communities. Meanwhile a working definition of the "CF community" needs
to be "those who choose to use netCDF to store earth system data in a
self describing way" even though this initially disenfranchises those
who wish to use CF conventions for other data formats.

### 2.2 Funding 

There are four basic funding mechanisms that could support the
maintenance and development of the CF conventions:

1.  Institutional Subscription Mechanisms: Institutions could form a
    consortium, funded by membership subscription, which would fund
    specific activities (with the Open Geospatial Consortium as a
    possible role model).

2.  National Subscription Mechanisms: CF could be sponsored by major
    international programmes (for example, the World Climate Research
    Programme) allowing national funding agencies to provide support in
    accordance with international commitments.

3.  Benevolent Organisations: some key interested parties could dedicate
    staff time to the CF "project" as part (or all) of their normal
    duties.

4.  Marginal Activities: interested parties working on CF in their
    "spare" time.

Currently all CF development is funded by the fourth of these options,
which means that CF development is not responsive enough, and it is
leading to untenable workloads for the key players.

Questions that have been raised concerning the first two funding
approaches listed above include:

1.  How would decisions be made to deploy the funding?

2.  In the case of the CF Consortium: who would hold the cash? Could the
    financial management be separated from the scientific
    decision-making?

3.  How would the CF community become involved with national programmes?

Given the right community management structure, a combination of funding
approaches could be used, and indeed given where CF is now, a
combination of these approaches is inevitable during what will have to
be a transition phase.

In the near future an element of funding from benevolent organisations
is expected. Expressions of commitment to support parts of CF
development have been received from Unidata, from the Program for
Climate Model Diagnosis and Intercomparison (PCMDI), and from the NERC
Centres of Atmospheric Science (NCAS): Unidata may assist with the
community interface, PCMDI will provide support for the CF development
process, and the NCAS/British Atmospheric Data Centre (BADC) will be
contributing direct support for standard name maintenance, development
and evolution. However, even with this extra support, CF will not be
able to evolve as it needs, and other funding arrangements will be
necessary. Such arrangements will not be possible without visible
leadership, accountability and formal encoding of the process of
governance

### 2.3 Management 

In keeping with the past development of the CF standard, the GO-ESSP
participants strongly favoured a continued consensus-based governance
procedure. Wide participation should be encouraged with input sought
from individuals representing a variety of disciplines, perspectives,
and geographical locations. Individual influence on CF\'s future should
be commensurate with the value of suggestions made and independent of
funding.

There is a strong desire within the existing CF community that,
regardless of funding, the evolution of CF should be carried out with
due process. Accordingly, we propose 1) that a collection of reference
files, illustrating correct CF encoding and suitable for the testing of
data-reading applications be maintained at every stage and 2) that CF
modifications occur in a manner that conforms to the following sequence:

1.  Requests for modification to CF are proposed to the community.

2.  A period of community discussion is entered into, including
    consideration of the relationship of CF to other standards.

3.  A provisional resolution is described as a consensual agreement.

4.  Reference files incorporating the proposed features are produced.

5.  Where the proposed modifications have non-trivial implications for
    implementation in software, trial implementations will be carried
    out. Trial implementations will be tested on both existing and new
    versions of the CF reference files, to check that new features can
    be correctly interpreted without detriment to backwards
    compatibility. A public evaluation and assessment of experiences
    will follow.

6.  If problems emerge, the process is repeated from step 2; otherwise
    ...

7.  Consensus decision is made to accept the proposed changes as
    provisional changes to the standard and to advertise these changes
    to the community (indicating that advanced implementers may want to
    begin using them).

8.  Multiple proposed changes are evaluated as a package in order to
    implement an orderly version control strategy.

9.  Consensus decisions should finalise the release of new versions of
    CF.

10. The test reference files should then become part of the corpus of
    test data for future revisions.

The process will be different in detail for modifications (usually
additions) to the standard name table on the one hand, and to the CF
standard on the other. The former are more numerous, require faster
turn-round, but generally do not involve wide community debate or trial
implementations; an appropriate turn-round time is one month. For the
latter, three months would be more realistic.

We also propose the establishment of two standing CF committees, the
membership of which would be open to those with significant interest and
time to commit to taking CF forward:

1.  Conventions Committee, to be responsible for developing changes to
    the CF standard, and to include (but not be limited to)
    representatives of those who have reference implementations, who can
    provide feedback on the practicality of CF initiatives and
    validation of tools which wish to be described as "CF-compliant".

2.  Standard Name Committee, to be responsible for adding standard names
    to the CF convention and working towards interoperability with other
    vocabulary maintainers.

Although CF must remain community-driven, its continuity can only be
assured if some formally established board, responsive to community
needs, assumes responsibility. Accordingly, it is also proposed that a
CF panel be established under the governance of relevant major
international programmes, which would be expected to appoint all or
nearly all nominees to membership. The next section discusses the
establishment of such a panel.

In view of their responsibility to the community, the membership of the
committees will be advertised on the CF website. The job of the
committee members will be to take an active interest in the community
debate on new developments (process outlined above), participating
personally where appropriate. On behalf of the community, the committees
will take the required decisions within their respective remits by
consensus among their own membership in cases where community consensus
is not evident because public debate is inconclusive.

Each of the CF committees will include a permanent funded member of
staff, viz. the manager of CF standard names and the manager of CF
conventions. Both individuals must be skilled technical document
editors, as their primary duty will be the maintenance of the CF
standard documents. The latter will mostly likely be a software
engineer, able to appreciate issues involved in both data processing and
models. The former needs an understanding of modern metadata frameworks
and a broad scientific interest, since to deal with requests for new
standard names (often coming from those who are not themselves the
scientists responsible for producing the data) it is necessary to
understand what the quantities are and to get to become familiar with
the terminology in various fields. If past experience is a guide, the
development of CF will depend largely on these two individuals, who will
be the first point of call for requests for modifications and who will
carry the process forward by their own contributions to discussions and
by deploying appropriate technology to facilitate community involvement.
In particular, it will be part of their job to provide reference files
and implementations. Although the responsibility will lie with the
committees corporately, the other members will probably have only
part-time involvement and the vagaries of their individual workloads
should not be allowed to preclude timely progression of CF. The lack of
anyone with time to carry out the role of manager of CF conventions over
the last year or so, for example, has meant that several significant
developments have been agreed on the CF email list but not yet
implemented in the standard (extension to cell_methods, standard_name
parameters, relation of formula_terms and bounds, relation of forecast
and validity time).

In both committees we recommend that

-   Insofar as possible, the principle of "no consensus, no change"
    should be followed (but reflecting that agreement may not always be
    possible, majority voting by committees may be necessary)

-   The chair should be elected to serve for a period of three years,
    although the membership should be self-selected. Where and when
    possible, the secretarial function should be funded.

-   Insofar as possible, a geographical distribution of members should
    be encouraged -- partly by nominating potential candidates to
    self-select as required.

Other ad-hoc groups may be needed to consider various issues such as
those listed in the Appendix One. Such areas, while heavily overlapping
with the CF core, may involve developing branches of CF which may
initially be in conflict. Such conflicts will need to be resolved
through a community discussion at the committee level.

### 2.4 Responsibility and Stewardship

As outlined above, a formal governance framework is also desirable.
There are a number of possible candidate organisations which could
provide a framework, but reflecting the heritage of CF, we here
recommend that initially the World Climate Research Programme\'s
(WCRP\'s) Working Group on Coupled Modeling (WGCM) take formal
responsibility for CF.

The WGCM and Working Group on Numerical Experimentation (WGNE) have been
established to work together and with the international climate and
weather modeling communities to establish \"an integrated approach to
climate modelling in the WCRP.\" Part of their charge is to promote
coordinated experimentation, which requires sharing data among centres.
For the sharing of climate model output, the format of choice has
usually been netCDF, and in some recent WGCM-coordinated projects, the
CF-conventions for metadata have been adopted (e.g., simulations in
support of the IPCC\'s Fourth Assessment Report).

The WGCM has expressed interest in data standards for climate model
output and has been kept abreast of the CF-developments. Recent
discussions at the Ninth Session of the WGCM led to an invitation to the
original CF authors to formally request appointment of a panel that
under the WGCM would provide oversight for the governance of the CF
conventions. It is therefore proposed that the WGCM establish a CF
Governance Panel charged with the following responsibilities

-   Assure the viability and vitality of the Conventions Committee and
    the Standard Name Committee by:

    -   Formally appointing members from those self-nominated and by
        periodically reviewing the membership (this would also provide
        at least some formal recognition of the voluntary work done by
        committee members).

    -   Making changes to the terms of reference of the committees by
        consensus with the committee membership.

-   Promote and help integrate CF across WCRP programs and the broader
    programs of WCRP\'s sponsors (ICSU, WMO, and IOC). In particular the
    panel would attempt to influence developing WMO metadata standards
    so that they gracefully accommodate the CF conventions.

-   Encourage continued support of CF by benevolent organizations, guide
    the deployment of such spending, and explore additional funding
    mechanisms as required.

The WGCM will appoint members of the panel, which would specifically
include (but not necessarily be limited to) representatives from: 1) the
WGCM, 2) groups contributing significant resources in support of CF (as
currently anticipated from Unidata, PCMDI, and NCAS), and 3) the chairs
of the Conventions Committee and Standard Name Committee described in
section 2.3 above. Although this panel would be responsible for
stewardship of CF, it would not have any special responsibility for or
influence on its technical content.

As CF usage widens, it may be necessary to consider alternative parent
bodies (to the WGCM) for the CF governance panel, to provide alternative
funding strategies and/or better represent community expectations of
governance. Accordingly, both the WGCM and CF panel will regularly
review whether other governance strategies would be more effective.

.

## 3. Next Steps

The two main priorities in the near future are to spread the load of CF
management by making better use of technology (including website, issue
tracking etc) to exploit the existing in-kind contributions, and to
agree upon a strategy for establishing longer term funding stream to
support CF activities. The WGCM\'s CF Panel needs to be established. At
the same time, the community needs to buy into the future management
structures outlined here (or suggest alternatives). The GO-ESSP meeting
proposed a formal timetable to achieve that buy-in and move from the
current situation to a new community managed framework:

1.  Community discussion should follow the appearance of this paper
    (done).

2.  One month after this paper appears, community discussion closes, and
    the existing CF authors decide whether the community response
    requires a different approach from that outlined here.. (done,
    approved)

3.  Aa committee structure based on section 2.3 should be set up with
    initial chairs selected by the existing CF authors. Potential
    members should be invited to nominate themselves for appointment by
    majority vote of the CF authors and committee chairs.

4.  .

5.  The first order of business of the new committees should be to
    define the changes in content for CF-1.1 and outline the priorities
    for further work.

6.  The managers of CF standard names and conventions should be
    appointed as soon as funding has been secured. (done)

7.  The draft terms of reference for the committees (appendix two)
    should be approved.

Throughout this process, interested parties should lobby any or all
national or international bodies that could provide ongoing funding for
CF maintenance and development.

## Appendix One: Current and Future Issues for CF

There are a large number of issues which need addressing in the near
future, some of which have the potential for requiring divergence in the
CF conventions, and this is partly why an effective CF governance
structure is needed.

Issues include:

1.  **Supporting technology:** To help facilitate CF development,
    several suggestions have been made, including: 1) integrating the
    mailing list with forum software to allow better development of
    discussion threads; 2) assigning version numbers to the evolving
    conventions to indicate both major and minor changes; 3) updating
    and improving the website, including documentation of the reasons
    for any changes or additions to the CF conventions; 4) developing
    further rudimentary tools to check for CF compliance and to
    encourage \"best practices\".

2.  **Staggered and unstructured grids**: While the CF convention
    supports storing data on staggered grids, and indeed on irregularly
    spaced grids, it does it in a rather simple manner which permits the
    data to be used by any software - this is an advantage - but does
    not record any high-level information about the "construction" of
    the grids. This is not fully supportive of the wide range of new
    grids which are being proposed (e.g. the Yin/Yang grid) and may make
    efficient storage of the data relatively awkward. Proposals now on
    the table suggest for the first time that grid information may need
    to be stored in different files from that of the data which, while
    not strictly in accord with CF's status as a netCDF convention, may
    be needed for practical reasons and is an approach already supported
    by some software. There is also an increasing need to describe
    unstructured hydrodynamic and watershed models which use meshes
    consisting of triangles, quadrilaterals and mixtures of polygons.
    Different issues arise, such as how to describe the indexing methods
    and connectivity of meshes, and there is a wealth of experience
    within the structures developed by engineering community to draw
    upon

3.  **GIS information content:** Interoperability experiments are
    underway in a number of places, aiming to both deliver netCDF data
    into Geographical Information Systems (GIS) and to store data
    originating from GIS systems in netCDF. In both cases there are
    technical issues to resolve about how to deal with differing
    standard descriptions and how they map onto the other.

4.  **Ontologies and nomenclature:** CF parameters are fully described
    by supplementing their standard names with additional descriptive
    information stored as attributes of the netCDF variables. Other
    ontologies categorise their information differently, e.g. by
    including coordinate information (such as "surface" or "daily
    maximum") as part of the parameter description. Such differences
    complicate the establishment of equivalence tables. Existing
    standard names identify only those quantities normally produced or
    inferred from climate models; measured parameters (such as radar
    signal strength) are currently not supported. It has been suggested
    that CF could exploit the XML namespace concept to allow parameters
    to be included from named and linked external vocabularies (or
    dictionaries) which would help with extending the domain of CF. Such
    external vocabularies would have to be well managed, comprehensive,
    and have reliable futures to avoid risks associated with,
    incomplete, imprecise or duplicate definitions and atrophy. Where CF
    might come to depend on external vocabularies, it would be important
    to have establish clear understandings between external vocabulary
    maintainers and the CF community on how the sets of vocabularies
    would evolve. CF could also investigate the concept of "scope" for
    standard names, to allow regionally important standard names without
    global agreement -- this would of course have to be done with care
    to avoid fragmentation. CF also needs to revisit the issue of
    standard names that have an implied or explicit singleton vertical
    dimension (for example, the use of surface and 1.5m in standard
    names is not consistent).

5.  **NetCDF-4**: CF-1.0 is based on the netCDF-3 data model, and to
    some extent reflects the limitations of that model. netCDF-4
    introduces an expanded model, allowing, for instance, for ragged
    dimensions and hierarchical groups of data. The CF-1.0 data model
    will remain compatible with netCDF-4; however, it may be more
    natural to express some features of CF using the expanded model. Is
    it appropriate or necessary to assume the netCDF-4 data model in
    subsequent revisions of CF?

6.  ***In situ* observations (profiles, time series and trajectories):**
    The existing CF documents describe how station data might be encoded
    in CF compliant files in a way which is satisfactory for climate
    model output. For in-situ observations, it is potentially rather
    inconvenient and inefficient, and alternatives have been proposed,
    perhaps using new features of netCDF-4.

7.  **Discovery information:** While CF describes the data encoded, it
    does not include "discovery information", that is, information which
    allows the user to discriminate between two otherwise identical
    datasets (for example, two model simulations). There are a large
    number of potential discovery content standards, and supporting the
    information to populate one or more of them in CF attributes would
    be desirable.

8.  **Modularisation and compliance**: It is not yet clear what "CF
    compliance" means, even though it is clear that it will mean
    different things for datasets and software. Since a great deal of CF
    is optional, compliance cannot mean that all features are actually
    used. It has been suggested that CF could be broken into modules
    each of which could be version controlled, allowing software to
    claim compliance to specific components of the CF conventions rather
    than the whole edifice. Since archived data cannot easily be changed
    once written, backward compatibility for the conventions is a
    serious issue -- should it be an inviolable principle (as it has
    been so far)?

9.  **CF dialects:** As the diversity of uses of CF grows, the need may
    arise for "varieties" of the standard to be developed for different
    applications. Because most of CF is optional, this is not generally
    a problem; it simply means that metadata needed in one discipline
    will not be used in another. However, a more difficult issue arises
    where a structure which suits one variety of data is quite
    unsuitable in another, or where a mandatory feature is too onerous
    (for instance because it requires too much space for metadata
    storage). Since so many needs are in common, it would generally be
    better for interoperability and ease of maintenance to develop a
    single CF standard, but if it has incompatible dialects, the
    circumstances in which they should be used will have to be carefully
    defined.

10. **Automatic Processing:** CF needs to build tools to support
    variable naming from standard names after processing. For example, a
    derivate with respect to time of an east-west coordinate should lead
    to a standard name which is mappend onto a velocity.

## Appendix Two: Terms of Reference for Committees and Panel

Aims of the CF standard

The CF standard for climate and forecast metadata is designed to promote
the processing and sharing of files created with the netCDF API. The
conventions define metadata that provide a definitive description of
what the data in each variable represents, and of the spatial and
temporal properties of the data. This enables users of data from
different sources to decide which quantities are comparable, and
facilitates building applications with powerful extraction, regridding,
and display capabilities.

Principles of design of the CF standard

Data should be self-describing. No external tables are needed to
interpret CF files. For instance, CF encodings do not depend upon
numeric codes.

Conventions are developed only for known issues. Instead of trying to
foreseethe future, features are added as required.

The convention should be easy to use, for both writers and users of
data.

The metadata and the semantic meaning encoded through the metadata
should be readable by humans as well as easily utilized by programs.

Redundancy should be minimised as much as possible (so as to reduce the
chance

of errors or inconsistency when writing data).

Constitution of the CF panel

The CF panel will come into existence on 1st September 2006 and assume
its duties and responsibilities from that date. Until that date, the
original CF authors will have responsibility for the government of the
CF standard.

The CF panel will be appointed by the WMO/WCRP Working Group on Coupled
Modelling (WGCM) to govern the development of the CF standard on behalf
of the user community. If the WGCM wishes to transfer or share
responsibility for CF with another permanent committee of an
international organisation, it may decide to do so with the agreement of
both CF committees.

The CF panel will include, but not be limited to, members of the WGCM,
representatives of organisations contributing significant resources in
support of CF, and the chairs of the CF committees on conventions and
standard names.

Terms of reference of the CF panel

The CF panel will be responsible for the stewardship of CF, but will not
have any special responsibility for or influence on the technical
content of CF.

The CF panel will ensure that its own constitution and terms of
reference, those of the CF committees, and the aims and general
principles of design of the CF standard are published. These may be
altered by the CF panel only after appropriate public debate and with
the agreement of both CF committees.

The CF panel will promote and help integrate the use of CF across WCRP
programmes and the broader programmes of WCRP\'s sponsors (ICSU, WMO,
and IOC). In particular the panel will attempt to influence developing
metadata standards of WMO and other international organisations so that
they accommodate the CF standard.

The CF panel will encourage continued support of CF by benevolent
organisations and explore additional funding mechanisms if necessary.

The CF panel will appoint people who have nominated themselves or agreed
to serve as members of the conventions committee and the standard names
committee. In doing so it will have regard to the expertise and
interests relevant to the remit of each committee and will attempt to
obtain representation of a variety of communities and a geographical
spread of members. The maximum and minimum numbers of members of either
committee may be amended by agreement between that committee and the CF
panel. The CF panel will ensure that the current membership of the two
CF committees is published.

Constitution of the CF committees

Anyone with sufficient time, interest and expertise is qualified to
serve as an ordinary member of the conventions committee or the standard
names committee or both. Prospective ordinary members will nominate
themselves. Before 1st September 2006, members of the committees will be
appointed by the original CF authors. From 1st September 2006, they will
be appointed by the CF panel. Members judged by the CF panel to have
been inactive for an extended period will be asked to resign. Members
may choose to resign at any time and must retire after five years, but
may be reappointed. The maximum number of ordinary members of each
committee is sixteen and the minimum is four.

The initial chairs of the committees will be appointed by the original
CF authors. Whenever a vacancy arises subsequently, each committee will
elect its own chair from among its ordinary members. The chair may
resign the office at any time and must retire after three years, but may
be reelected.

Each committee will have authority and responsibility for the
development of the aspects of the CF standard within its remit, as
detailed in its terms of reference, having regard to the aims and
general principles of design of CF. It will discharge its responsibility
by overseeing and contributing to public debate on how the standard
should be expanded or altered, and by deciding after debate whether and
what changes will be made.

Each committee will be assisted in its responsibility by a permanent and
funded member of staff, who will be appointed in a manner decided by the
CF panel, and who will be an ex-officio member of the committee and its
secretary. The manager of CF conventions will be the secretary of the
conventions committee and the manager of CF standard names will be the
secretary of the standard names committee. The committee will propose
priorities for work by its secretary.

Each committee will ensure that appropriate means are made available for
making proposals and carrying out debates in a way which is visible and
open to participation by all interested parties, and for retaining a
permanent public record of debates and of any decisions made by the
committee. It will decide the period of time which should be allowed
between a proposal being made publicly and a final decision being
required, and any other procedures necessary. These procedures should
assume that community consensus will generally be followed in deciding
for or against changes, but the committee will make the decision itself
if no consensus is evident or the public debate is inconclusive. The
committee may decide exceptionally to make no change although public
consensus is in favour of a change, if it judges that the proposed
change would be damaging to the CF standard. A committee member who
believes this to be case for a particular proposed change should notify
the other members of this opinion before the time arrives by which a
decision must be made according to the rules, and may request the
committee to take the decision itself, rather than allowing public
consensus to decide. If such a request is not made, the secretary will
decide what is the outcome of the public debate and will make or not
make changes accordingly.

A decision by the committee on changes to the CF standard within its
remit or on any procedural matter will require a simple majority of the
membership to be in favour.

The committees may not devolve responsibility for the CF standard to
other bodies, but they may encourage the formation of other permanent or
temporary ad-hoc groups to debate issues and propose developments to CF.

Each committee will ensure that the parts of the standard for which it
is responsible, any supporting documents and resources, and the
procedures for proposing and deciding changes are kept up-to-date and
made publicly available.

The committees may not change their constitutions or terms of reference
themselves, but each may propose changes to be made by the CF panel.

Terms of reference of the conventions committee

The conventions committee will be responsible for the development of the
CF conventions constituting the CF netCDF standard, except for the
definition of standard names and of any other aspects of controlled
vocabulary in the appendices to the standard that it agrees with the
standard names committee should be within the remit of that committee.

The conventions committee and standard names committee will together
define the format of the standard name table.

The conventions committee will have an interest in implementation of CF
metadata conventions corresponding to the CF standard in other file
formats and media apart from netCDF.

The conventions committee will be responsible for the CF conformance
document and for deciding what CF conformance means.

The membership of the conventions committee should include
representatives of those who maintain widely used software which follows
the CF conventions, especially those which the committee regards as
reference implementations.

Terms of reference of the standard names committee

The standard names committee will be responsible for the definition of
CF standard names and of any other aspects of controlled vocabulary in
the appendices to the CF netCDF standard that it agrees with the
conventions committee should be within its remit.

The standard names committee will be responsible for maintaining the
standard name table. The standard names committee and the conventions
committee will together define the format of the standard name table.

The standard names committee will have an interest in working towards
interoperability with other vocabulary maintainers.

The standard names committee will make proposals for modification of
conventions when it appears that names cannot be satisfactorily defined
within the prevailing conventions.

The membership of the standard names committee should include
representatives of the various scientific user communities of the CF
standard.

[^1]: NCAS/British Atmospheric Data Centre, Rutherford Appleton
    Laboratory, U.K.

[^2]: Program for Climate Model Diagnosis and Intercomparison, Lawrence
    Livermore National Laboratory, U.S.A.

[^3]: National Center for Atmospheric Research, U.S.A.

[^4]: NCAS/Centre for Global Atmosphere Modelling, University of
    Reading, U.K.

[^5]: NOAA Pacific Marine Environmental Laboratory, U.S.A.

[^6]: British Oceanographic Data Centre, Proudman Oceanographic
    Laboratory, U.K.

[^7]: Unidata, University Corporation for Atmospheric Research, U.S.A.

[^8]: <http://www.cgd.ucar.edu/cms/eaton/cf-metadata/> as of July 5,
    2004, describing CF-1.0

[^9]: <http://www.cgd.ucar.edu/cms/eaton/cf-metadata/clivar_article.pdf>
    as of July 5, 2004, document dated November 6, 2003.