Climate and Forecast Metadata Conventions
Encyclopedia
The Climate and Forecast (CF) metadata
conventions are conventions for the description of Earth sciences data, intended to promote the processing and sharing of data file
s. The metadata defined by the CF conventions are generally included in the same file as the data, thus making the file "self-describing". The conventions provide a definitive description of what the data values found in each netCDF
variable represent, and of the spatial and temporal properties of the data, including information about grids, such as grid cell bounds and cell averaging methods. This enables users of files from different sources to decide which variables are comparable, and is a basis for building software applications with powerful data extraction
, grid remapping, data analysis
, and data visualization
capabilities.
Standards Process Group (SPG) and others as more broadly applicable standards
.
output data collected for Coupled model intercomparison project
s, which are the basis of Intergovernmental Panel on Climate Change
assessment reports .
They are promoted as an important element of scientific community coordination by the World Climate Research Programme
. They are also used as a technical foundation for a number of software packages and data systems, including the Climate Model Output Rewriter (CMOR), which is post processing software for climate model data, and the Earth System Grid
, which distributes climate and other data . The CF conventions have also been used to describe the physical fields transferred between individual Earth system model software components, such as atmosphere and ocean components, as the model runs
.
data, in the atmosphere, ocean, and other physical domains. It was designed primarily to address gridded data types such as numerical weather prediction
model outputs and climatology
data in which data binning
is used to impose a regular structure
. However, the CF conventions are also applicable to many classes of observational data and have been adopted by a number of groups for such applications.
, but its structure is general and it has been adapted for use with other data formats. For example, using the CF conventions with Hierarchical Data Format
data has been explored .
Specific CF metadata descriptors use values of attributes to represent
A central element of the CF Conventions is the CF Standard Name Table. The CF Standard Name Table uniquely associates a standard name with each geophysical parameter in a data set, where each name provides a precise description of physical quantities being represented. Note that this is the string value of the
As an example of the information provided by CF standard names, the entry for sea-level atmospheric pressure includes:
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
conventions are conventions for the description of Earth sciences data, intended to promote the processing and sharing of data file
Data file
A data file is a computer file which stores data to use by a computer application or system. It generally does not refer to files that contain instructions or code to be executed , or to files which define the operation or structure of an application or system ; but specifically to information...
s. The metadata defined by the CF conventions are generally included in the same file as the data, thus making the file "self-describing". The conventions provide a definitive description of what the data values found in each netCDF
NetCDF
NetCDF is a set of software libraries and self-describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. The project homepage is hosted by the Unidata program at the University Corporation for Atmospheric Research...
variable represent, and of the spatial and temporal properties of the data, including information about grids, such as grid cell bounds and cell averaging methods. This enables users of files from different sources to decide which variables are comparable, and is a basis for building software applications with powerful data extraction
Data extraction
Data extraction is the act or process of retrieving data out of data sources for further data processing or data storage...
, grid remapping, data analysis
Data analysis
Analysis of data is a process of inspecting, cleaning, transforming, and modeling data with the goal of highlighting useful information, suggesting conclusions, and supporting decision making...
, and data visualization
Data visualization
Data visualization is the study of the visual representation of data, meaning "information that has been abstracted in some schematic form, including attributes or variables for the units of information"....
capabilities.
History and Evolution
The CF conventions were introduced in 2003, after several years of development by a collaboration that included staff from U.S. and European climate and weather laboratories . The conventions contained generalizations and extensions to the earlier Cooperative Ocean/Atmosphere Research Data Service (COARDS) conventions and the Gregory/Drach/Tett (GDT) conventions . As the scope of the CF conventions grew along with its user base, the CF community adopted an open governance model . In December 2008 the trio of standards, netCDF+CF+OPeNDAP, was adopted by IOOS as a recommended standard (number 08-012) for the representation and transport of gridded data. The CF conventions are being considered by the NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Standards Process Group (SPG) and others as more broadly applicable standards
.
Applications and User Base
The CF conventions have been adopted by a wide variety of national and international programs and activities in the Earth sciences . For example, they were required for the climate modelClimate model
Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate...
output data collected for Coupled model intercomparison project
Coupled model intercomparison project
In climatology, the Coupled Model Intercomparison Project is the analog of AMIP for global coupled ocean-atmosphere general circulation models. CMIP began in 1995 under the auspices of the Working Group on Coupled Modeling , which is in turn under auspices of CLIVAR and the Joint Scientific...
s, which are the basis of Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
assessment reports .
They are promoted as an important element of scientific community coordination by the World Climate Research Programme
World Climate Research Programme
The World Climate Research Programme was established in 1980, under the joint sponsorship of International Council for Science and the World Meteorological Organization, and has also been sponsored by the Intergovernmental Oceanographic Commission of UNESCO since 1993. It is a component of the...
. They are also used as a technical foundation for a number of software packages and data systems, including the Climate Model Output Rewriter (CMOR), which is post processing software for climate model data, and the Earth System Grid
Earth System Grid
The Earth System Grid is a data distribution portal whose development is funded mainly by the United States Department of Energy. It is the portal through which the Program for Climate Model Diagnosis and Intercomparison at Lawrence Livermore National Laboratory is distributing data for the IPCC...
, which distributes climate and other data . The CF conventions have also been used to describe the physical fields transferred between individual Earth system model software components, such as atmosphere and ocean components, as the model runs
.
Supported Data Types
CF is intended for use with state estimation and forecastingForecasting
Forecasting is the process of making statements about events whose actual outcomes have not yet been observed. A commonplace example might be estimation for some variable of interest at some specified future date. Prediction is a similar, but more general term...
data, in the atmosphere, ocean, and other physical domains. It was designed primarily to address gridded data types such as numerical weather prediction
Numerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
model outputs and climatology
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
data in which data binning
Data binning
Data binning is a data pre-processing technique used to reduce the effects of minor observation errors. The original data values which fall in a given small interval, a bin, are replaced by a value representative of that interval, often the central value...
is used to impose a regular structure
. However, the CF conventions are also applicable to many classes of observational data and have been adopted by a number of groups for such applications.
Supported Data Formats
CF originated as a standard for data written in netCDFNetCDF
NetCDF is a set of software libraries and self-describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. The project homepage is hosted by the Unidata program at the University Corporation for Atmospheric Research...
, but its structure is general and it has been adapted for use with other data formats. For example, using the CF conventions with Hierarchical Data Format
Hierarchical Data Format
Hierarchical Data Format is the name of a set of file formats and libraries designed to store and organize large amounts of numerical data...
data has been explored .
Design Principles
Several principles guide the development of CF conventions:- Data should be self-describing, without external tables needed for interpretation.
- Conventions should be developed only as needed, rather than anticipating possible needs.
- Conventions should not be onerous to use for either data-writers or data-readers.
- Metadata should be readable by humans as well as interpretable by programs.
- Redundancy should be avoided to prevent inconsistencies when writing data.
Specific CF metadata descriptors use values of attributes to represent
- Data provenance:
title,institution,contact,source(e.g. model),history(audit trail of operations),references,comment - Description of associated activity:
project,experiment - Description of data:
units,standard_name,long_name,auxiliary_variables,missing_value,valid_range,flag_values,flag_meanings - Description of coordinates:
coordinates,bounds,grid_mapping(withformula_terms); time specified withreference_time("time since T0") andcalendarattributes. - Meaning of grid cells:
cell_methods,cell_measures, and climatological statistics.
A central element of the CF Conventions is the CF Standard Name Table. The CF Standard Name Table uniquely associates a standard name with each geophysical parameter in a data set, where each name provides a precise description of physical quantities being represented. Note that this is the string value of the
standard_name attribute, not the name of the parameter. The CF standard name table identifies over 1,000 physical quantities, each with a precise description and associated canonical units. Guidelines for construction of CF standard names are documented on the conventions web site.As an example of the information provided by CF standard names, the entry for sea-level atmospheric pressure includes:
- standard name:
air_pressure_at_sea_level - description: sea_level means mean sea levelSea levelMean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, which is close to the geoidGeoidThe geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest , and extended through the continents . According to C.F...
in sea areas. Air pressure at sea level is the quantity often abbreviated as MSLP or PMSL. - canonical units: Pa