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1. Learn about ERA-Interim data

  1. Read What is ERA-Interim.
  2. Browse the ERA-Interim catalogue and make sure the data you are interested in is available in ERA-Interim. A demonstration (for ERA5 but the same principle applies for ERA-Interim) is available as part of the video tutorial below:

    Full Transcript (pdf)

  3. Read the ERA-Interim data documentation and take note of the parameters (fields) you want to use, and of the corresponding values for data type, stream, level type (surface, pressure levels, model levels, etc) base time and forecast steps.

2. User account and License agreement

  1. The ERA-Interim data is hosted at ECMWF. To access the ERA-Interim data you need a user account with ECMWF, so if you do not have a account, register a ECMWF account now.
  2. Read the Conditions of Use and accept the agreement at the bottom the page. This is necessary so we have a record of you accepting the license agreement.

3. Download a data sample

ECMWF provides a web interface to quickly download a sample dataset for evaluation.

  1. Go to ECMWF Web User Interface for ERA-Interim
  2. Make sure you are logged in with your ECMWF user ID (top right of the page)
  3. In the left hand menu select if you want daily or monthly data, and surface, pressure levels or model levels
  4. Select the time period you want to download. Since October 25th 2017,  the time period you can select for daily data is limited to one month, and for monthly data to one year.
  5. Select Time and Step options
  6. Select the parameters you want to download data for
  7. On the next page, if you are shown a data license, review and accept the data licence
  8. The data can be downloaded in the GRIB file format or in NetCDF. NetCDF is experimental and unsupported. Select the desired format.
  9. On the next page you are shown a summary of your data request. Review it, and at this stage you may also change the output grid resolution and also select a specific geographical area of interest. Once you are ready to proceed with the download, click "Retrieve Now".
  10. Once the data is retrieved you are shown a download link, click it to download the data.
  11. It can take up to a few hours to extract the data from the archives, depending on demand and on the size of your data request. If you don't want to wait you can come back later, check the status of your request in your Job List, and download the data from there.  After three days the data is deleted from our servers.
  12. With the download link you are shown a technical summary of your data request. We recommend you copy this to a text document and keep it for your own documentation.

Please note also that the web user interface does not list all available data. For listings of all available data please see the ECMWF archive catalogue (which allows you to browse through the entire ERA-Interim archive) and the ERA-Interim documentation.

3. Further downloads

For operational data downloads you should not use the sampling web interface. Instead, you should download data using Python scripts.

You need:

  • A computer with a *nix operating system is highly recommended. Microsoft Windows is known to work too, but is unsupported, see here for details.
  • The Python programming language. If you do not have it installed yet, install Python now.

4. Set up your computer

This is to configure your computer to programmatically retrieve data from ECMWF. You only need to do this once, and only if you have never retrieved ECMWF data using Python before. For more information refer to Access ECMWF Public Datasets of ECMWF WebAPI.

1. Install the ECMWF WebAPI client library by running:

 

sudo pip install https://software.ecmwf.int/wiki/download/attachments/56664858/ecmwf-api-client-python.tgz


If you cannot use the sudo pip command above (e.g. no admin rights on your machine), use the --user option of pip to install it in $HOME/.local/lib :


pip install --user https://software.ecmwf.int/wiki/download/attachments/56664858/ecmwf-api-client-python.tgz


2. Get and install an ECMWF API key:

  1. Go to https://apps.ecmwf.int/auth/login/ to verify you are logged in. If you are not, log in with your ECMWF account details (as registered in step 2).

  2. Go to https://api.ecmwf.int/v1/key/ . You will see something like below:

 

{
    "url"   : "https://api.ecmwf.int/v1",
    "key"   : "XXXXXXXXXXXXXXXXXXXXXX",
    "email" : "john.smith@example.com"
}

3. Copy the bit with the curly brackets as shown above into a text file and save the file as $HOME/.ecmwfapirc (on Unix/Linux) or %USERPROFILE%\.ecmwfapirc (on Windows)

5. Run a test

This is to verify that your computer is set up correctly.

1. Copy the following Python script to a text file and save it, for example as 'my_ERA-Interim_test_script.py'

#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer

server = ECMWFDataServer()
server.retrieve({
    "class": "ei",
    "dataset": "interim",
    "expver": "1",
    "stream": "oper",
    "type": "fc",
    "levtype": "sfc",
    "param": "167.128",
    "date": "2017-08-01/to/2017-08-31",
    "time": "00:00:00",
    "step": "3",
    "grid": "0.75/0.75",
    "target": "my_ERA-Interim_test_file.grb",
 })

2. Run the script. On most computers you would do this by opening a command prompt and typing

python my_ERA-Interim_test_script.py

The test request will download data from ECMWF and save as file 'my_ERA-Interim_test_file.grb' in the directory you issued the command from.

Note that the data retrieval is not designed to be instant. The test request above usually takes a few minutes to complete, but depending on demand can take longer.

3. With your favourite GRIB file reader verify that you can read the file. If you are not familiar with GRIB please see What are GRIB files and How to read or decode a GRIB file

If you get an error message or the output is not as specified in to the Python script, most likely your computer setup is wrong, or you did not accept the ERA5 license, so please go back to the previous steps.

6. Create your data retrieval script

  1. Browse the ERA-Interim data catalogue for the data you are interested in, and in the last step make a selection in all boxes and click 'View the MARS request'. This shows a template Python script with your selected options.
  2. Copy the Python script to a text file and save it, for example as 'my_ERA-Interim_script_v1.py'
  3. If necessary, adapt the Python script to your requirements,e.g. change date, time and grid.
    1. For an output in netcdf format, specify "format" as "netcdf"
    2. If you specify "format" as "netcdf", then you also need to set "grid" e.g. "grid": "0.3/0.3". Otherwise, GRIB to netCDF conversion will fail.
    3. If you specify "grid", the horizontal resolution is in decimal degrees. If not set, the archived grid as specified in the data documentation is used i.e. reduced Gaussian grid
    4. To subset to a geographical area, specify "area" as N/W/S/E in geographic lat/long degrees. Southern latitudes and western longitudes must be given as negative numbers e.g. "area": "75/-20/10/60". Requires "grid" to be set to a regular grid e.g. "grid": "0.3/0.3".

    5. Change the "target": "CHANGEME", to the desired output path and file name, e.g. "data1.nc" or "./data/data1.grib". The default path is the current working directory.

Limitations:

  • You can have a maximum of three active requests at a time.
  • The maximum data volume is 20GB per request.
  • The maximum number of fields to be retrieved is 600,000 fields per request.

Note that the data retrieval is not designed to be instant. A larger request can take hours and even days to complete.

To retrieve data efficiently (and get your data quicker!) you should retrieve all the data you need from one tape, then from the next tape, and so on. In most cases this means retrieving all the data you need for one month, then for the next month, and so on. See ERA-Interim Retrieval efficiency pages.

7. Run your data retrieval script

On most computers you would do this by opening a command prompt and typing

python my_ERA-Interim_script_v1.py

This will retrieve the data as specified and download it as a single file to your computer into the current directory (or whichever "target" directory you specified).

For long running processes you can check the progress of your request in your job list.

8. Check results

Check that the data you downloaded meets your requirements.

To report an issue or bug please contact Copernicus Support at ECMWF

 

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