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The CDS offers seamless web-based and API-based search and retrieve facilities to access climate data and information.In addition, the CDS also provides a generic software toolbox that allows users to develop web-based applications that make use of the datasets available in the CDS.
The data provided by the CDS are free and open data, subject to the user agreeing to the relevant dataset licence(s). For further details, please see this article from the ECMWF Newsletter 151.
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Please note: CDS datasets are covered by one or more licences, and users have to accept them in order to download datasets (whether through the web interface, or the CDS API, or the toolbox). At the time this article was written, the acceptance of the relevant licences can only be carried out through the CDS web interface for the relevant dataset. In some cases, data can has multiple licenses because it comes from different providers. |
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- Accepted. Each request is assigned a unique ID and a priority. The priority is chosen according to different criteria, such as the origin of the request (CDS web interface/API/Toolbox). For example, the CDS web interface usually has higher priority because it is an interactive application and users expect an immediate response to their request..
- In progress. The request is being fulfilled and the data is being collected from the archive.
- Failed. The request encountered problems.
- Unavailable. The data has expired from cache and therefore cannot be retrieved at the current time. In this case the request should be resubmitted.
- Succeded. The resulting data file is ready to download.
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- Where the data are actually stored can make a significant difference in performance. CDS data hosted in 'MARS internal' is stored on CDS disks, and so is faster to retrieve. The 'MARS external' datasets are stored in the ECMWF MARS (tape) archive, and in this case it is important to request as much data as possible from the same tape file in your CDS request.
- Submit small requests over very large and heavy requests. This will ensure your requests are not penalised in the CDS request queue. In particular:
For ERA5 data requests, please see: How to download ERA5. The first example in CDS API examples section below shows how to efficiently download a whole year of hourly data for 2m temperature (grib format, for an area subset) from the CDS, by asking for one month of data per request.
- For C3S seasonal forecast data requests, please see: Recommendations and efficiency tips for C3S seasonal forecast datasets.
- For UERRA data requests, please see: UERRA retrieval efficiency.
- When using the CDS API or the CDS Toolbox, it is advised that users take as an example the API request or toolbox request script shown at the bottom of the CDS web 'Download data' page for the dataset of interest, and use this as the basis for your request.
- Some ERA5 datasets, such as
reanalysis-era5-complete, do not appear in the CDS catalogue on the web interface, but users can still retrieve the data through the CDS API. In these cases, users can make use of a subset of the ECMWF MARS keywords in their CDS API request, and should also follow the MARS efficiency rule of thumb (the idea is to request as much data as possible from the same tape file or to reduce the number of tapes involved.). - Users are strongly advised to check the allowed and not allowed keywords from the relevant dataset webform.
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