Version 1.7.2 DRAFT, 28 March, 2014

Original Authors

Brian Eaton

NCAR

Jonathan Gregory

Hadley Centre, UK Met Office

Bob Drach

PCMDI, LLNL

Karl Taylor

PCMDI, LLNL

Steve Hankin

PMEL, NOAA

Additional Authors

John Caron

UCAR

Rich Signell

USGS

Phil Bentley

Hadley Centre, UK Met Office

Greg Rappa

MIT

Heinke Höck

DKRZ

Alison Pamment

BADC

Martin Juckes

BADC

Andrew Walsh

METOC

John Graybeal

TBD

Many others have contributed to the development of CF through their participation in discussions about proposed changes.

 

Abstract

This document describes the CF conventions for climate and forecast metadata designed to promote the processing and sharing of files created with the netCDF Application Programmer Interface [NetCDF]. 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.

The CF conventions generalize and extend the COARDS conventions [COARDS]. The extensions include metadata that provides a precise definition of each variable via specification of a standard name, describes the vertical locations corresponding to dimensionless vertical coordinate values, and provides the spatial coordinates of non-rectilinear gridded data. Since climate and forecast data are often not simply representative of points in space/time, other extensions provide for the description of coordinate intervals, multidimensional cells and climatological time coordinates, and indicate how a data value is representative of an interval or cell. This standard also relaxes the COARDS constraints on dimension order and specifies methods for reducing the size of datasets.


Table of Contents

Preface
1. Introduction
1.1. Goals
1.2. Terminology
1.3. Overview
1.4. Relationship to the COARDS Conventions
2. NetCDF Files and Components
2.1. Filename
2.2. Data Types
2.3. Naming Conventions
2.4. Dimensions
2.5. Variables
2.5.1. Missing Data, valid and actual range
2.6. Attributes
2.6.1. Identification of Conventions
2.6.2. Description of file contents
3. Description of the Data
3.1. Units
3.2. Long Name
3.3. Standard Name
3.4. Ancillary Data
3.5. Flags
4. Coordinate Types
4.1. Latitude Coordinate
4.2. Longitude Coordinate
4.3. Vertical (Height or Depth) Coordinate
4.3.1. Dimensional Vertical Coordinate
4.3.2. Dimensionless Vertical Coordinate
4.4. Time Coordinate
4.4.1. Calendar
4.5. Discrete Axis
5. Coordinate Systems
5.1. Independent Latitude, Longitude, Vertical, and Time Axes
5.2. Two-Dimensional Latitude, Longitude, Coordinate Variables
5.3. Reduced Horizontal Grid
5.4. Timeseries of Station Data
5.5. Trajectories
5.6. Grid Mappings and ProjectionsHorizontal Coordinate Reference Systems, Grid Mappings, and Projections
5.6.1. Use of the CRS Well-known Text Format
5.7. Scalar Coordinate Variables
6. Labels and Alternative Coordinates
6.1. Labels
6.1.1. Geographic Regions
6.2. Alternative Coordinates
7. Data Representative of Cells
7.1. Cell Boundaries
7.2. Cell Measures
7.3. Cell Methods
7.3.1. Statistics for more than one axis
7.3.2. Recording the spacing of the original data and other information
7.3.3. Statistics applying to portions of cells
7.3.4. Cell methods when there are no coordinates
7.4. Climatological Statistics
8. Reduction of Dataset Size
8.1. Packed Data
8.2. Compression by Gathering
9. Discrete Sampling Geometries
9.1. Features and feature types
9.2. Collections, instances and elements
9.3. Representations of collections of features in data variables
9.3.1. Orthogonal multidimensional array representation
9.3.2.  Incomplete multidimensional array representation
9.3.3.  Contiguous ragged array representation
9.3.4. Indexed ragged array representation
9.4. The featureType  attribute
9.5. Coordinates and metadata
9.6. Missing Data
A. Attributes
B. Standard Name Table Format
C. Standard Name Modifiers
D. Dimensionless Vertical Coordinates
E. Cell Methods
F. Grid Mappings
G. Revision History
H. Annotated Examples of Discrete Geometries
H.1. Point Data
H.2. Time Series Data
H.2.1. Orthogonal multidimensional array representation of time series
H.2.2. Incomplete multidimensional array representation of time series
H.2.3. Single time series, including deviations from a nominal fixed spatial location
H.2.4. Contiguous ragged array representation of time series
H.2.5. Indexed ragged array representation of time series
H.3. Profile Data
H.3.1. Orthogonal multidimensional array representation of profiles
H.3.2. Incomplete multidimensional array representation of profiles
H.3.3. Single profile
H.3.4. Contiguous ragged array representation of profiles
H.3.5. Indexed ragged array representation of profiles
H.4. Trajectory Data
H.4.1. Multidimensional array representation of trajectories
H.4.2. Single trajectory
H.4.3. Contiguous ragged array representation of trajectories
H.4.4. Indexed ragged array representation of trajectories
H.5. Time Series of Profiles
H.5.1. Multidimensional array representations of time series profiles
H.5.2. Time series of profiles at a single station
H.5.3. Ragged array representation of time series profiles
H.6. Trajectory of Profiles
H.6.1. Multidimensional array representation of trajectory profiles
H.6.2. Profiles along a single trajectory
H.6.3. Ragged array representation of trajectory profiles
Bibliography

List of Tables

3.1. Supported Units
3.2. Flag Variable Bits (from Example)
3.3. Flag Variable Bit 2 and Bit 3 (from Example)
A.1. Attributes
C.1. Standard Name Modifiers
E.1. Cell Methods
F.1. Grid Mapping Attributes

List of Examples

3.1. Use of standard_name
3.2. Instrument data
3.3. A flag variable, using flag_values
3.4. A flag variable, using flag_masks
3.5. A flag variable, using flag_masks and flag_values
4.1. Latitude axis
4.2. Longitude axis
4.3. Atmosphere sigma coordinate
4.4. Time axis
4.5. Perpetual time axis
4.6. Paleoclimate time axis
5.1. Independent coordinate variables
5.2. Two-dimensional coordinate variables
5.3. Reduced horizontal grid
5.4. Timeseries of station data
5.5. Trajectories
5.6. Rotated pole grid
5.7. Lambert conformal projection
5.8. Latitude and longitude on a spherical Earth
5.9. Latitude and longitude on the WGS 1984 datum
5.10. British National Grid
5.11. British National Grid + Newlyn Datum in CRS WKT format
5.12. Multiple forecasts from a single analysis
6.1. Several parcel trajectories
6.2. Northward heat transport in Atlantic Ocean
6.3. Model level numbers
7.1. Cells on a latitude axis
7.2. Cells in a non-rectangular grid
7.3. Cell areas for a spherical geodesic grid
7.4. Methods applied to a timeseries
7.5. Surface air temperature variance
7.6. Mean surface temperature over land and sensible heat flux averaged separately over land and sea.
7.7. Thickness of sea-ice and snow on sea-ice averaged over sea area.
7.8. Climatological seasons
7.9. Decadal averages for January
7.10. Temperature for each hour of the average day
7.11. Extreme statistics and spell-lengths
7.12. Temperature for each hour of the typical climatological day
7.13. Monthly-maximum daily precipitation totals
8.1. Horizontal compression of a three-dimensional array
8.2. Compression of a three-dimensional field
B.1. A name table containing three entries
H.1. Point data.
H.2. Timeseries with common element times in a time coordinate variable using the orthogonal multidimensional array representation.
H.3. Timeseries of station data in the incomplete multidimensional array representation.    
H.4. A single timeseries.
H.5. A single timeseries with time-varying deviations from a nominal point spatial location
H.6. Timeseries of station data in the contiguous ragged array representation.
H.7. Timeseries of station data in the indexed ragged array representation.
H.8. Atmospheric sounding profiles for a common set of vertical coordinates stored in the orthogonal multidimensional array representation.
H.9. Data from a single atmospheric sounding profile.
H.10. Atmospheric sounding profiles for a common set of vertical coordinates stored in the contiguous ragged array representation.
H.11. Atmospheric sounding profiles for a common set of vertical coordinates stored in the indexed ragged array representation.
H.12. Trajectories recording atmospheric composition in the incomplete multidimensional array representation.
H.13. A single trajectory recording atmospheric composition.
H.14. Trajectories recording atmospheric composition in the contiguous ragged array representation.
H.15. Trajectories recording atmospheric composition in the indexed ragged array representation.
H.16. Time series of atmospheric sounding profiles from a set of locations stored in a multidimensional array representation.
H.17. Time series of atmospheric sounding profiles from a set of locations stored in an orthogonal multidimensional array representation.
H.18. Time series of atmospheric sounding profiles from a single location stored in a multidimensional array representation.
H.19. Time series of atmospheric sounding profiles from a set of locations stored in a ragged array representation.
H.20. Time series of atmospheric sounding profiles along a set of trajectories stored in a multidimensional array representation.
H.21. Time series of atmospheric sounding profiles along a trajectory stored in a multidimensional array representation.
H.22. Time series of atmospheric sounding profiles along a set of trajectories stored in a ragged array representation.