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In the table below some practical details of the data is shown including the base year period covered and the number of ensemble members. Hindcast and forecast periods are not distinguished here as they are not mentioned in the CDS form neither. Please note that the ensemble members are not available individually, but they are concatenated into one file while the data is downloaded. Generally users are encouraged to use all members instead of selecting one members of the predictions.
| Forecast period | Ensemble members | Nominal resolution | |
|---|---|---|---|
| CMCC (Italy) | 1960-2020 | 10 | 100 km |
| HadGEM3 (UK) | 1960-2020 | 10 | 100 km |
| EC-EARTH (Europe) | 1960-2020 | 10 | 100 km |
| MPI-ESM1-2-HR (Germany) | 1960-2018 | 10 | 100 km |
| MPI-ESM1-2-LR (Germany) | 1960-2021 | 21 | 250 km |
Start-Date Ensembles
The DCPP experiments published in the CDS, are a suite of overlapping simulations that are initialised every year throughout the duration of the start-date range specified by the experiment. The simulations begin in November to allow for DJF (December, January, February) seasonal averages to be calculated. There are 10 (16) simulations (ensemble members) for each start-date (called "Base year" in he CDS form).
The start-date ensemble is reflected in the DCPP data naming convention with the addition of a s<yyyy> start-date ensemble identifier ahead of the conventional CMIP6 ripf ensemble identifiers. For example, a simulation with a start year of 2014 will have the start-date ensemble identifier s2014, and a full ensemble identifier that follows the pattern s2014-r<W>i<X>p<Y>f<Z> where W, X, Y and Z are positive integers.
See some more more details in the "In-file metadata modifications" section below.
Parameter listings
Data for the dcppA-hindcast experiments and the dcppB-forecast experiments will include parameters at monthly and daily resolution as described in the tables below. The parameter descriptions presented here are harvested from the CMIP6 Data Request via the CLIPC variable browser.
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- CF-Checks: The CF-checker tool checks that each NetCDF4 file in a given dataset is compliant with the Climate and Forecast (CF) conventions, compliance ensures that the files are interoperable across a range of software tools.
- PrePARE: The PrePARE software tool is provided by PCMDI (Program for Climate Model Diagnosis and Intercomparison) to verify that CMIP6 files conform to the CMIP6 data protocol. All CMIP6 data should meet this required standard however this check is included to ensure that all data supplied to the CDS have passed this QC test.
- nctime: The nctime checker checks the temporal axis of the NetCDF files. For each NetCDF file the temporal element of the file is compared with the time axis data within the file to ensure consistency. For a time-series of data comprised of several NetCDF files nctime ensures that the entire timeseries is complete, that there are no temporal gaps or overlaps in either the filename or in the time axes within the files.
- Errata: The dataset is checked to ensure that no outstanding Errata record exists.
- Data Ranges: A set of tests on the extreme values of the variables are performed, this is used to ensure that the values of the variables fall into physically realistic ranges.
- Handle record consistency checks: This check ensures that the version of the dataset used is the most recently published dataset by the modelling centre, it also checks for any inconsistency in the ESGF publication and excludes any datasets that may have an inconsistent ESGF publication metadata.
- Exists at all both partner sites: It is asserted that each dataset exists at all two both partner sites DKRZ and IPSL.
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Some updates have been applied to the DCPP netCDF files in the CDS. These conform with the CF Metadata Conventions and improve the usability of the time dimension when multiple overlapping decadal experiments are used together with different start dates (adding additional time coordinates facilitates to use multiple datasets in parallel and enables unambiguous selection of time). This will make the calculation of multi-model ensembles more straightforward. The specific details of the updates include the following modifications:
- A “realization” variable is added, to represent the ensemble member
- The “sub_experiment_id” global attribute is adjusted to include the start year and month of the simulation
- A “reftime” variable is added, representing the start time of the simulation
- A “leadtime” coordinate variable is added: this is calculated from the “reftime” plus and the valid times from the existing time variable
- The "long_name" attribute of the "time" coordinate is updated to "valid_time".
Citation information
The CMIP6 data Citation Service provides information for data users on how to cite CMIP6 DCPP data and on the data license. Available CMIP6 data citations are discoverable in the ESGF or in the Citation Search at: http://bit.ly/CMIP6_Citation_Search (search for DCPP at the top of the page).
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Subsetting and downloading data
CDS users will now be are able to apply subsetting operations to CMIP6 decadal datasets. This mechanism (the "roocs" WPS framework) that runs at each of the partner sites: DKRZ and IPSL. The WPS can receive requests for processing based on dataset identifiers, a temporal range, a bounding box and a range of vertical levels. Each request is converted to a job that is run asynchronously on the processing servers at the partner sites. NetCDF files are generated and the response contains download links to each of the files. Users of the CDS will be able to make subsetting selections using the web forms provided by the CDS catalogue web-interface. More advanced users will be able to define their own API requests in the CDS Toolbox that will call the WPS. Output files will be automatically retrieved so that users can access them directly within the CDS.
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