ERA5T is a meteorological re-analysis dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 dataset. In this project, the ERA5T data is sourced with the following setup:
| Topic | Description |
|---|---|
| Data type | gridded |
| Horizontal coverage | global |
| Horizontal resolution | 0.25°x0.25° (i.e. ~30x30km²) |
| Temporal coverage | 1979 to present day |
| Temporal resolution | monthly |
| File format | netCDF |
| Update frequency | daily, with a lag of ~5 days, see paragraph below |
| Available variables | see this table |
Among a plethora of available variables (see here for an example and here for the variable descriptions), the following subset is selected:
| Abbreviation | Variable name |
|---|---|
| ci | Sea-ice cover fraction (0-1) |
| sp | Surface pressure (Pa) |
| sst | Sea surface temperature (K) |
| z70 | Geopotential height at 70 hPa height (m²/s²) |
The relevance of these variables for the project is described in detail in Wang et al. (2017).
This aspect becomes critical for operational forecasting. The initial released data with no more than three months behind real time, is called ERA5T. For the CDS, daily updates are available 5 days behind real time and monthly mean updates are available 5 days after the end of the month. For netCDF data, there is no means of differentiating between ERA5 and ERA5T data. The original data information is available here.
You need to use cdsapi (i.e., ECMWF's API) in order to download ERA5 data. Read CDS API documentations for more details. In short, a (free) registration to Copernicus and the setting up of ECMWF's API are required. Both steps are easily done, see the sketch below:
If not already done in the virtual environment, execute pip install cdsapi
Your $HOME/.cdsapirc file shall contain:
url: https://cds.climate.copernicus.eu/api/v2
key: <your key>If you need help on the API on how to source specific data, go here, select the desired data and then click on show API request. Here are some code examples to retrieve daily data. Whether a variable belongs to analysis or forecast is answered here.