Comparison of selected surface level ERA5 variables against in‐situ observations in the continental Arctic

Abstract

In this study, data from 17 ground‐based, continental Arctic observatories are used to evaluate the performance of the European Centre for Medium‐Range Weather Forecasts Reanalysis version 5 (ERA5) reanalysis model. Three aspects are evaluated: (i) the overall reproducibility of variables at all stations for all seasons at one‐hour time resolution; (ii) the seasonal performance; and (iii) performance between different temporal resolutions (one hour to one month). Performance is evaluated based on the slope, R2 value, and root‐mean‐squared error (RMSE). We focus on surface meteorological variables including 2‐m air temperature (temperature), relative humidity (RH), surface pressure, wind speed, zonal and meridional wind speed components, and short‐wave downward (SWD) radiation flux. The overall comparison revealed the best results for surface pressure (0.98 ± 0.02, R2mean ± standard deviation [σR2]), followed by temperature (0.94 ± 0.02), and SWD radiation flux (0.87 ± 0.03) while wind speed (0.49 ± 0.12), RH (0.42 ± 0.20), zonal (0.163 ± 0.15) and meridional wind speed (0.129 ± 0.17) displayed poor results. We also found that certain variables (surface pressure, wind speed, meridional, and zonal wind speed) showed no seasonal dependency while others (temperature, RH, and SWD radiation flux) performed better during certain seasons. Improved results were observed when decreasing the temporal resolution from one hour to one month for temperature, meridional and zonal wind speed, and SWD radiation flux. However, certain variables (RH and surface pressure) showed comparatively worse results for monthly resolution. Overall, ERA5 performs well in the Arctic, but caution needs to be taken with wind speed and RH, which has implications for the use of ERA5 in global climate models. Our results are useful to the scientific community as it assesses the confidence to be placed in each of the surface variables produced by ERA5.