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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:
   
   

   Multimedia
   name Final-ERA5.mp4 width 20% height 20%

   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.

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License agreement

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Read the Conditions of Use and accept the agreement at the bottom the page

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3. Download a data sample

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For operational data downloads you should not use the sampling web interface. Instead, you should download data using the ECMWF Web-API (with 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:

Before proceeding with the steps below, users must be ECMWF registered and have their computer set up as described on How to download data via the ECMWF WebAPI (steps 1-4)

4. Run an ERA-Interim test retrieval script

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"
}

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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"test.py'"

Code Block
language 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/2017-08-3103", "time": "00:00:00", "step": "3", "grid": "0.75/0.75", "area":"75/-20/10/60", "format":"netcdf",   "target": "my_ERA-Interim_test_file.grbnc", })

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

Code Block
language py
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' "test.nc" in the directory you issued the command from. The file should be around 58 KB.

If you get an error message, most likely your computer setup is wrong, or you did not accept the data license, please go back to the previous set-up steps.

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 it 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.

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If it all worked fine, you are now ready to retrieve the data you need by following the instructions below

5. Create your data retrieval script

1. Browse As a starting point, 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 template Python script to a text file and save it, for example as 'my_ERA-Interim_script_v1.py'.
3. If necessary, adapt Adapt the template Python script to your requirements, e.g. change date, time and grid.
   taking the following remarks into account:
   1. In most cases, you will have to add lat/lon "grid" in your script,
   2. For an output in netcdf format, specify "format" as "netcdf"
   3. If you specify "format" as "netcdf", then you also need to set "grid" e.g., "grid": "1.0.3/0.3". Otherwise, GRIB to netCDF conversion will fail/1.0". This will enable you to download data on a regular lat/lon grid. And this is necessary if you download the data in NetCDF format.
   4. For an output in NetCDF format, add "format": "netcdf" in your script. By default, output will be in GRIB format. Notice if you retrieve forecast data in NetCDF, please be aware of this potential issue.
   5. If you specify specify "grid", the horizontal resolution is in decimal degrees. For more details, see this link. If not set, the archived grid as specified in the data documentation is used i.e. reduced Gaussian grid
   6. If you do not want global data, you can add To subset to a geographical area, specify "area" asN/W/S/E in geographic lat/long lon degrees. Southern latitudes and western longitudes must be given as negative numbers, e.g., "area": "75/-20/10/60". Requires If you set "grid" to be set to a regular grid area", you should also add a lat/lon grid, e.g., "grid": "1.0/1.3/0.3".Change the 0", as shown in c. For more details about "area", seethis link.
   7. If you are retrieving forecast data ("type":"fc"), make sure that "steps" are specified. Note that if "type" is set to "fc", then "time" is the time of the forecast.
   8. 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.

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. Run your data retrieval script

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

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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).

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

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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