CDS

Downloading Data Sets from Copernicus’s Climate Data Store

Copernicus.eu provides a set of interesting data sets for research, education, and applied earth sciences on their Climate Data Store (CDS). Among the different data sets there is the latest ECMWF high-resolution reanalysis data set which replaces ERA Interim (which was ERA-4; version 4). The R package ecmwfr provides a convenient interface to download these data sets.

Before Downloading Data

Before you will be able to download any data you need to get a free personal account.

• Register yourself for CDS services
• Terms and conditions

To retrieve data ecmwfr use wf_set_key()to add the login details to your local keyring (requires the R package keyring).

Once you are in possession of your personal user (namely your user ID and a secret key) ecmwfr allows to send requests to CDS and/or download the data.

The Request Syntax

CDS data retrievals are based on a list object which specifies the data set to be downloaded. These definitions are called requests (for those who are familiar with mars: these are basically mars requests). A request defined the type of the dataset, the variables to be downloaded, the time period, output format, target location, a custom area extent, and other details.

The request syntax is available for a range of different CDS data sets. Check the CDS Dataset website to see a list of available datasets and to check whether API requests are allowed or not (go to Download Data, select some data, show request by clicking Show API Request (red button, bottom of page).

# Specify the data set
request <- list("dataset"        = "reanalysis-era5-pressure-levels",
                "product_type"   = "reanalysis",
                "variable"       = "temperature",
                "pressure_level" = "850",
                "year"           = "2000",
                "month"          = "04",
                "day"            = "04",
                "time"           = "00:00",
                "area"           = "70/-20/30/60",
                "format"         = "netcdf",
                "target"         = "era5-demo.nc")

# Start downloading the data, the path of the file
# will be returned as a variable (ncfile)
ncfile <- wf_request(user = "2088",
                      request = request,   
                      transfer = TRUE,  
                      path = tempdir(),
                      verbose = FALSE)

Date period specification

For those familiar to ECMWFs mars syntax: CDS does not accept date = "2000-01-01/to/2000-12-31" specifications at the moment. It is possible to specify one specific date via date = "2000-01-01" or multiple days via date = ["2000-01-01","2000-01-02","2000-10-20"] but not via ".../to/...".