NetCDF Climate and Forecast (CF) Metadata Conventions

Version 1.3, 7 November, 2008

Original Authors

Brian Eaton


Jonathan Gregory

Hadley Centre, UK Met Office

Bob Drach


Karl Taylor


Steve Hankin


Additional Authors

John Caron


Rich Signell


Phil Bentley

Hadley Centre, UK Met Office

Greg Rappa


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



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

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
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
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
5.7. 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
7.4. Climatological Statistics
8. Reduction of Dataset Size
8.1. Packed Data
8.2. Compression by Gathering
A. Attributes
B. Standard Name Table Format
C. Standard Name Modifiers
D. Dimensionless Vertical Coordinates
E. Cell Methods
F. Grid Mappings
G. Revision History

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. 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. Climatological seasons
7.7. Decadal averages for January
7.8. Temperature for each hour of the average day
7.9. Temperature for each hour of the typical climatological day
7.10. 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