Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim

We compare the main atmospheric drivers of the melt season over the Greenland Ice Sheet (GrIS) in ERA5 and ERA-Interim (ERAI) in their overlapping period 1979-2018. In summer, ERA5 differs significantly from ERAI, especially in the melt regions. Small-scale ERA5 - ERAI differences near the ice sheet's margins and over steep slopes can be explained by the different resolution, while the large-scale differences indicate a different representation of physical processes in the two reanalyses: averaged over the lower parts of the GrIS, the mean near-surface air temperature is 1 K lower, while the mean downward shortwave radiation at the surface is on average 15 W m - 2 higher than in ERAI. Comparison with observational weather station data shows a significant warm bias in ERAI and, for ERA5, a significant positive bias in downward shortwave radiation. Consequently, methods that previously estimated the GrIS surface mass balance from the ERAI surface energy balance need to be carefully recalibrated before converting to ERA5 forcing.