As stated on the parameters page, the BADC archives the ECMWF ERA-40 data in its original format (GRIB) and grid types. These are the N80 Reduced Gaussian Grid for surface data and at T159 Spectral Resolution for upper air data.
The main reasons for keeping the data in these representations are (i) to maintain an archive of the original data and (ii) to keep the data in its most compressed format (both reduced gaussian and spectral resolutions are more efficient than a regular latitude/longitude grid).
However, we appreciate that many users will wish to obtain the data in a more convenient regular latitude/longitude grid and we have developed tools to make these available. For users only wishing to access a small amount of the ERA-40 data they can make use of the BADC Live Access Server (LAS) which allows sub-setting, plotting, animations and output to NetCDF format. The BADC LAS is currently under development but will be released soon.
Users wishing to access large volumes of ERA-40 data on a regular latitude/longitude grid will need to use the ERA-40 Data Selector (also currently under development). This service will allow you to submit a data request to the BADC. Our automated data converter will then convert the request data to a regular grid, group (tar) and compress (gzip) files if required and then inform you where to collect the data from.
Please note that the regular gridded ERA-40 data is produced when requested by users. This is because the full dataset (if converted to NetCDF) would be 10s of terrabytes in volume. By storing the data in a more efficient format the data is all held on disk and is therefore more accessible to users.
This means that already the BADC LAS and ERA-40 Data Selector present the data as already present in our archive, it is actually a virtual dataset, parts of which are created via user requests. We have designed a Caching Architecture to create, store, delete and manage the virtual datasets.
Regular latitude/longitude datasets are available in the following resolutions:
Please be patient with the system. Multiple users may all be requesting the creation of particular files concurrently. Our computers are working as fast as they can to deliver the data to you. We will aim to provide you with a delivery time estimate to keep you informed at all times.
In order to provide data conversion and delivery at the request of the user the BADC has developed a caching system that is called when the user asks for some data (via either the BADC LAS or the ERA-40 Data Selector). A list of the required original files is produced and this is sent to the cache processor. For more information, please see our animated slide of how the caching system works.
The cache is interrogated to find out if the regular gridded equivalents of the original files are already present. If not, they are created and stored in the cache. Otherwise, they are delivered directly. The cache manager makes sure that old files are deleted and that the cache does not exceed its volume limit.
The cache manager also evaluates the size of your request and will do one of the following depending on the volume of data you ask for:
The BADC LAS provides a multi-functional web-interface to large geospatial datasets. It is particularly suited to global gridded data such as the ERA-40 Re-analyses. If you would like to find out more about the freely available LAS software please visit the NOAA website.
Users registered for the ERA-40 data held at the BADC can log in to the BADC LAS to extract subsets of the dataset. All model levels and parameters are available and all data has been transformed to a 1° x 1° grid (this was the favoured resolution in a user questionnaire). The BADC LAS allows data sub-setting in latitude, longitude, altitude and time. The output can be obtained in a number of formats including gif and postscript image files, or NetCDF data files. A limited animation facility is also available.
Please note that the LAS intended for users with low data volume requirements. If it recieves large requests it will ignore them and inform you that it is doing so. Moderate to high data volume users should use the ERA-40 Data Selector in preference to the BADC LAS.