What's wrong?

In January 2019, a problem was identified regarding the following data in the climate data store (CDS):

CDS Dataset

ERA5 hourly data on pressure levels from 1979 to present

Parameters affectedU-component of wind, V-component of wind
LevelAll pressure levels
Time periods affected

All ERA5 pressure-level winds of product type Reanalysis and Ensemble members

Only exactly at the poles (i.e., where latitude is 90N or 90S), the values of the U and V components of the wind are far too low. Values are close to zero, rather than several m/s. At all other locations the winds are unaffected.

This problem is caused by the way these winds were determined from Vorticity and Divergence in spherical harmonics representation (the native model representation) when interpolated to a regular grid in the Climate Data Store.

What can I do?

Instead, please use winds at neighbouring locations at 89.75 (N/S) and 89.5 (N/S)  for Reanalysis and Ensemble members winds, respectively.

Will the issue be fixed?

No, it is currently not anticipated that this will be resolved.

The problem is limited to two grid points (North pole and South pole).

This document has been produced in the context of the Copernicus Climate Change Service (C3S).

The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.

The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.