Comprehensive evaluation of multi-source reanalysis datasets for surface atmospheric parameters over the Greenland Ice Sheet

The Greenland Ice Sheet is losing mass at an accelerating rate. In situ observations are sparse due to its harsh environment, making reanalysis datasets an essential alternative. However, their accuracy over Greenland―particularly in high-altitude and inland regions―remains uncertain, necessitating a systematic evaluation. In this study, we comprehensively evaluate four major reanalysis products―ERA5, ERA5-Land, MERRA-2 and NCEP/DOE R2―using observational data from 51 automatic weather stations across the Greenland Ice Sheet. We analyse accuracy in five key atmospheric variables (2 m air temperature, surface pressure, 10 m wind speed, downwelling shortwave and longwave radiation) across three temporal resolutions: monthly, daily and hourly. The results show that over the evaluation period (2018–2022), ERA5 and MERRA-2 consistently outperform the other considered products. ERA5 performs the best in temperature and pressure, with monthly temperature and pressure biases below 2.5 ℃ and 6 hPa, respectively, and strong consistency across time scales; at the same time, MERRA-2 exhibits the best accuracy in shortwave radiation in certain seasons, with hourly downwelling shortwave radiation correlation coefficients exceeding 0.92 in all four seasons, mainly because its aerosol and radiation processes better capture seasonal variability in atmospheric clarity and solar energy reaching the surface. ERA5-Land, despite its finer resolution, systematically underestimates summer shortwave radiation levels and features inconsistent wind speed accuracy. NCEP/DOE R2 shows pronounced errors across all variables and is not recommended for use in modern climate studies. Spatial analyses further reveal that the considered reanalysis products show the best accuracy along the coast and lower accuracy in the high-elevation interior. These findings offer essential guidance for the selection of suitable reanalysis products in climate and surface mass balance studies on Greenland.