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HadCRUT4: Version Numbering Scheme

HadCRUT4 Version Numbering

A new version numbering scheme has been introduced with the most recent update of the HadCRUT4 dataset. The HadCRUT4 version numbers take the following format:

The uses of X, Y, Z and θ in the versioning scheme are as follows:

- Major dataset version number. For HadCRUT4 this number is 4.
- Major update to methodology, code or source data. For example, Y would be updated with the inclusion of data sources that were not previously present in the dataset, such as the inclusion of a newly homogenised data source or if there is a major update or addition to the code used to produce the dataset.
- Minor update to methodology, code or source data. For example, Z would be updated when historical data sources already included in the dataset are updated (such as adding an extra year of data to an existing source that isn't updated on a monthly basis) or for minor updates to existing code.
- Reserved for future use.

Changes to the HadCRUT4 code or data sources will result in an update of the HadCRUT4 version number. Version numbering systems have also been implemented for the CRUTEM4 and HadSST3 datasets, the sources of land and sea data for HadCRUT4. Any version updates to these datasets will result in an update of the HadCRUT4 version number.

Version numbers are not increased with each monthly update of the dataset. Information on changes to data in monthly updates is described through use of field status flags.

Field Status Flags

Monthly updates to HadCRUT4 include updates to CRUTEM4 and HadSST3 data in a rolling 12 month update window running up to and including the most recent complete calendar month. Field status information is included in the meta data for monthly fields to indicate whether monthly fields are liable to change in future updates.

Finalised - "f"
- Monthly fields marked with a status flag of "f" are finalised and will not be updated again under the current HadCRUT4 version number.
Preliminary - "p"
- Monthly fields marked with a status flag of "p" are preliminary and may be updated in a future monthly update.

Application of version numbering to gridded data

The following data files are provided for the HadCRUT4 gridded data:

- Surface temperature anomalies for ensemble member 'E'.
- Uncertainties with no spatial or temporal correlation structure.
- Error covariance matrices for year 'yyyy'/month 'mm'.

The following auxiliary fields are also available:

- Gridded fields corresponding to the median ensemble member anomaly fields.
- The diagonal elements of the HadCRUT4 covariance matrices gridded onto a 5 degree latitude/longitude grid.

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