ERA5 monthly data

Hi all,

I am trying to get data from ERA5 on wind speed and direction at 100 m. I would like to know how the monthly datasets are derived, compared to the hourly datasets : is it the mean values (at each lcoation point) of the u and v wind component (10 min time steps) averaged on a month ? 

Indeed, when I derive the mean of the hourly values (of the Wind speed given by the u and v components) for a given month, the value is really different from the value of Wind speed derived from the monthly dataset. I know that calculating the amplitud of the Wind vector is not linear, so does someone have an advice to get monthly averaged Wind speed without downloading all the hourly values (at 100 m height) ?

Thanks !

Hi Julien,

Please see the updated link ERA5: How are the 100m winds calculated?



Hi Xiaobo,

I was trying to open 'ERA5: How are the 100m winds calculated?'. Unfortunately, the article seems to be not available anymore. Do you know where to receive a copy of it or where to find a new article about this topic?



Sorry Ron, the link was updated.


Hi Julien,

In ERA5 reanalysis data, the monthly means have been calculated from the hourly values. The monthly mean wind components are averages of the hourly wind components. The speed of these monthly mean components is not equal to the monthly mean wind speed. There is an article about this for the 10m ERA-Interim winds, but the same mathematical rules apply for ERA5 100m winds:

ERA-Interim Monthly Means of Daily Means: wind U and V versus 'wind speed'

For the 10m winds we do provide the monthly mean wind speed, but not for the 100m winds. I'm afraid you will have to download the hourly 100m wind data, calculate the hourly wind speed and then the monthly mean wind speed.

Note, that wind components are valid at the specified time, see the article:

Parameters valid at the specified time