Relative humidity data exceeds 100%

ERA5 relative humidity data on pressure levels above 500 hPa can exceeds 100%. This could be due to supersaturation with respect to ice at cold temperatures.

See the ERA5 IFS documentation (CY41R2), Part IV Physical processes, Chapter 7- Clouds and large-scale precipitation, for more information:

https://www.ecmwf.int/en/publications/ifs-documentation