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Initial release data, i.e. data no more than three months behind real time, is called ERA5T. In the event that serious flaws are detected in ERA5T, this data could be different to the final ERA5 data. Based on experience with the production of ERA5 so far (and ERA-Interim in the past), our expectation is that such an event would not occur often. So far, this has only occurred once:
- for the months September, October, November and at least a part of December 2021, the final ERA5 product is and will be different from ERA5T due to correction of the assimilation of incorrect snow observations in central Asia. Although the differences are mostly limited to that region and mainly to surface parameters, in particular soil moisture, all the resulting reanalysis fields do differ slightly over the whole globe. On the CDS disks, the initial fields have been and will be overwritten, i.e., for these months, access to the original CDS disk, ERA5T product is not possible after it has been overwritten.
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For the CDS, daily updates for ERA5T are available about 5 days behind real time and monthly mean updates are available about 5 days after the end of the month.
Note: At the moment, the timing of the availability of ERA5T data on the CDS on a daily basis can vary. We do not work to a specific target schedule. However, the D-5 data are typically available by 12UTC, but not guaranteed. We are working on reducing the variability of the time of availability, but this may take several months to achieve.
For MARS ERA5 data, monthly updates are available In the CDS, ERA5T data for a month is overwritten with ERA5 data about two months after the month in question.
For GRIB data, ERA5T can be identified by the key expver=0005 in the GRIB header. ERA5 is identified by the key expver=0001.
For netCDF data requests which return just ERA5 or just ERA5T data, there is no means of differentiating between ERA5 and ERA5T data in the resulting netCDF files.
For netCDF data requests which return a mixture of ERA5 and ERA5T data, the origin of the variables (1 or 5) will be identifiable in the resulting netCDF files. See the link for more detailsMARS ERA5 data, monthly updates are available about two months after the month in question.
The IFS and data assimilation
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In the CDS, there is the option of retrieving the data in netCDF format.
For GRIB data, ERA5T can be identified by the key expver=0005 in the GRIB header. ERA5 is identified by the key expver=0001.
For netCDF data requests which return just ERA5 or just ERA5T data, there is no means of differentiating between ERA5 and ERA5T data in the resulting netCDF files.
For netCDF data requests which return a mixture of ERA5 and ERA5T data, the origin of the variables (1 or 5) will be identifiable in the resulting netCDF files. See this link for more details.
Data organisation and how to download ERA5
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