ECMWF

Create ECMWF account

To be able to download data from ECMWF you first need to create an account with ECMWF. To do that go on the following site:

    https://www.ecmwf.int/user/login

Click on "Register" at the bottom. Fill the form and click on the big "Register" button at the end.

CDS API setup

Next you need to setup your CDS API personal access token. To do that follow the steps on the following page:

    https://cds.climate.copernicus.eu/how-to-api

Log in to your account.

You need to follow the steps for the "Linux users". All you need to do is step 1.3. :

    "Once logged in, copy the code displayed below to the file $HOME/.cdsapirc".

You need to create this file in the home of any of our internal servers. If you do not see a long (more than 30 character) string with numbers, letters and dashes in the blackish box you are probably not logged in. You need to be logged in to see this string. Then just create the file $HOME/.cdsapirc and copy-paste the full content of the blackish box into it.

Step 2. is already done. See below how to use our already installed CDS API client.

Accept license

When you download data for the first time you will be asked to accept a license. You need to to this just once.

• If you want to download data online directly from the web site you will see a button "Accept License" or similar to accept the license at the end of the field selection page. Just click on it.
• If you want to download data with a Python script - see below, the easiest way I found to accept the license is by starting(!) to download any field from the online web page. For example, from the following page:
      https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels?tab=download
  Log in and scroll down to the end of the page. There, under "Terms of use" you should see a red button saying "Accept License" or similar. Just click on it. That's all. No need to submit the request! Then downloading data with Python should work.
  

Load environment

To be able to use our common CDF API client you need to load:

Download data with Python

To download data from ECMWF with Python you have to write a Python script with a specific format. Have a look at point "3. Use the CDS API client for data access" of the following page for guidance:

    https://cds.climate.copernicus.eu/how-to-api

Another way to find out what to put in the script is to go on the web site, for example:

    https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels?tab=download

Select everything or an example of what you would like to download, scroll to the end of the page and click on "Show API request code". You can just copy paste the code you will see into your script and modify it to your liking.

Remember to load the Python environment above before executing your Python script!

Number of items limit

Note there is a limit for the number of "items" you can download in one request. According to Anabelle from the Copernicus User Support team:
    "This limit varies from dataset to dataset, as it depends on the granularity of the data served. For ERA5, 1 'item' corresponds to 1 variable on a (2D) field at 1 level at 1 timestep. Any request submitted to the CDS which is larger than the limit for that dataset will be rejected by the system, so you will need to modify you selection until it is smaller than the limit. If you go to the 'Download data' tab for a given dataset (e.g. ERA5), you can build a request interactively and you will get a warning if it exceeds the limit. Please note that these limits can change over time in order to balance the load on the system."

If your request gets too large you will have to split it up into multiple requests.