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Introduction
What are global climate projections?
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For pressure level data the model output is available on the pressure levels according to the table below. Note that since the model output is standardised not all models produce provide the data on the same pressure levels.
Frequency | Number of Levels | Pressure Levels (hPa) |
Daily | 8 | 1000., 850., 700., 500., 250., 100., 50., 10. |
Monthly | 17 | 1000., 925., 850., 700., 600., 500., 400., 300., 250., 200., 150., 100., 70., 50., 30., 20., 10. |
Ensembles
Each modelling centre typically run the same experiment using the same model several times to confirm the robustness of results and inform sensitivity studies through the generation of statistical information. A model and its collection of runs is referred to as an ensemble. Within these ensembles, three different categories of sensitivity studies are done, and the resulting individual model runs are labelled by three integers indexing the experiments in each category.
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Data
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A data availability matrix for the C3S CMIP5 exists at: https://cp-availability.ceda.ac.uk.
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Data Format
The CDS subset of CMIP5 data are provided as NetCDF files. NetCDF (Network Common Data Form) is a file format that is freely available and commonly used in the climate modelling community. See more details: What are NetCDF files and how can I read them
A CMIP5 NetCDF file in the CDS contains:
- Global metadata: these fields can describe many different aspects of the file such as
- when the file was created
- the name of the institution and model used to generate the file
- links to peer-reviewed papers and technical documentation describing the climate model,
- links to supporting documentation on the climate model used to generate the file,
- software used in post-processing.
- variable dimensions: such as time, latitude, longitude and height
- variable data: the gridded data
- variable metadata: e.g. the variable units, averaging period (if relevant) and additional descriptive data
The metadata provided in NetCDF files adhere to the Climate and Forecast (CF) conventions (v1.4 for CMIP5 data). The rules within the CF-conventions ensure consistency across data files, for example ensuring that the naming of variables is consistent and that the use of variable units is consistent.
File naming conventions
When you download a CMIP5 file from the CDS it will have a naming convention that is as follows:
<variable>_<cmor_table>_<model>_<experiment>_<ensemble_member>_<temporal_range>.nc
Where
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Format
The CDS subset of CMIP5 data are provided as NetCDF files. NetCDF (Network Common Data Form) is a file format that is freely available and commonly used in the climate modelling community. See more details: What are NetCDF files and how can I read them
A CMIP5 NetCDF file in the CDS contains:
- Global metadata: these fields can describe many different aspects of the file such as
- when the file was created
- the name of the institution and model used to generate the file
- links to peer-reviewed papers and technical documentation describing the climate model,
- links to supporting documentation on the climate model used to generate the file,
- software used in post-processing.
- variable dimensions: such as time, latitude, longitude and height
- variable data: the gridded data
- variable metadata: e.g. the variable units, averaging period (if relevant) and additional descriptive data
The metadata provided in NetCDF files adhere to the Climate and Forecast (CF) conventions (v1.4 for CMIP5 data). The rules within the CF-conventions ensure consistency across data files, for example ensuring that the naming of variables is consistent and that the use of variable units is consistent.
File naming conventions
When you download a CMIP5 file from the CDS it will have a naming convention that is as follows:
<variable>_<cmor_table>_<model>_<experiment>_<ensemble_member>_<temporal_range>.nc
Where
- variable is a short variable name, e.g. “tas” for ”temperature at the surface”
- cmor_table is a reference to the realm (an earth system component such as atmosphere or ocean) and frequency of the variable, e.g. “Amon” indicates that a variable is present in the atmosphere realm at a monthly frequency (link to list of these)
- model is the name of the model that produced the data
- ensemble member is the ensemble identifier in the form “r<X>i<Y>p<Z>”, X, Y and Z are integers
- the temporal range is in the form YYYYMM[DDHH]-YYYY[MMDDHH], where Y is year, M is the month, D is day and H is hour. Note that day and hour are optional (indicated by the square brackets) and are only used if needed by the frequency of the data. For example daily data from the 1st of January 1980 to the 31st of December 2010 would be written 19800101-20101231.
Please note that the CIMP5 filenames in the CDS do not contain a version tag as opposed to the file names used for the corresponding data in the ESGF nodes, where you have the versioning information. In the CDS we serve the latest version of the CMIP5 data which is now complete (no new version expected). To find the version number of this latest version published in the CDS, see the metadata of the netcdf file. This contains a track identity of the file and an http address for each file from where the version number information may be checked.
Quality control of the CDS-CMIP5 subset
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- Please note that not all the combinations of models and variables exist. This feature is inherited from the ESGF system, where the main target is to publish as much as possible data and even publish incomplete datasets, which might be of use. This allows to have more data available with the price that not everything is fully complete.
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreementAgreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The userusers thereof usesuse the information at itstheir sole risk and liability. For the avoidance of all doubtsdoubt , the European Commission and the European Centre for Medium - Range Weather Forecasts hashave no liability in respect of this document, which is merely representing the authorsauthor's view. |
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