Downloading ERA-Interim data for WRF

The ECMWF has a publicly accessible reanalysis dataset called ERA-Interim which can be used to run WRF. To download data for WRF, follow these steps:

1. Go to the ECMWF website: https://www.ecmwf.int/ and click the “Log in” link in the top right-hand corner.
2. If you already have an account, enter your username and password. If not, register by clicking “New users register here“. Fill in your name, UCD email address, Country: Ireland, Sector: Academic/Research. You will get an email with a link you need to click to confirm your application for an account. After a while you should receive another email with your ECMWF account details. Use these to log in, and change your password.
3. We need three different types of data to run WRF:
   • Invariant data (things that don’t change)
   • Surface data
   • Model Level data
4. We only need to download Invariant data once, which we can do here: http://apps.ecmwf.int/datasets/data/interim-full-invariant/. If you haven’t yet done so, click on “conditions of use”, fill in: Organisation: UCD, Organisation type: Academic/Research, Country: Ireland. If you agree with the conditions, click “Accept”. Select “Land-sea mask” and click “Retrieve GRIB”. Click “Retrieve now” on the next page, then you’ll see a page with the status of your request. When it changes from “queued” to “Download grib”, right-click on the download link and copy the link address. Open a terminal and ssh to the computer you will run WRF on (ORR2). If you need to, create a directory for this data. Mine is ~/GRIB/ERAI. Change into that directory, and use wget to download the data from the link you have copied. It will download with a strange name, like _mars-atls13-blahblah.grib, so move (mv) it to a sensible name, like ERA-Invariant.grib
5. We need to download Surface data for each forecast date, which we can do here: http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/.
   • Select the month you want (I’m getting December 2017).
   • In the “Select Time” box, select all: 00:00:00 06:00:00 12:00:00 18:00:00
   • In the “Select Step” box, select zero: 0
   • In the “Select parameter” box, select the following:- 2 metre dewpoint temperature
     – 2 metre temperature
     – 10 metre U wind component
     – 10 metre V wind component
     – Mean sea level pressure
     – Sea surface temperature
     – Sea-ice cover
     – Skin temperature
     – Snow density
     – Snow depth
     – Soil temperature levels 1, 2, 3, 4
     – Surface pressure
     – Volumetric soil water layer 1, 2, 3, 4
   • Click on the “Retrieve GRIB” button, then click on “Retrieve now”. This will bring you to a status page. When your download is ready, copy the link, wget it to ORR2 ~/GRIB/ERAI/ and give it a sensible name, like: ERA-SFC-201712.grib
6. Next we need the model level data, from here: http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=ml/. Select the same date, all times, and click on the following parameter names (which should tick all available levels):
   • Specific humidity
   • Temperature
   • U component of wind
   • V component of wind
     Then click on the “Retrieve GRIB” button, and “Retrieve now”. When the status of the request is complete, copy the “Download grib” link, wget to ORR2 and rename to something like: ERA-ML-201712.grib
     Finally, repeat the model level download procedure for one extra parameter, in a separate downloaded file:
   • Geopotential
     Download this file to ORR2 and rename to: ERA-MLZ-201712.grib

Your ERA-Interim files should now look something like this:

[conor@orr2 ERAI]$ ls -hl
total 346M
-rw-rw-r-- 1 conor conor 453K Mar 1 16:35 ERA-Invariant.grib
-rw-rw-r-- 1 conor conor 320M Mar 1 18:19 ERA-ML-201712.grib
-rw-rw-r-- 1 conor conor 1.4M Mar 2 13:12 ERA-MLZ-201712.grib
-rw-rw-r-- 1 conor conor 24M Mar 1 17:21 ERA-SFC-201712.grib