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

In this study, data from 17 ground-based, continental Arctic observatories areused to evaluate the performance of the European Centre for Medium-RangeWeather Forecasts Reanalysis version 5 (ERA5) reanalysis model. Three aspectsare evaluated: (i) the overall reproducibility of variables at all stations for allseasons 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,R2value, and root-mean-squarederror (RMSE). We focus on surface meteorological variables including 2-mair temperature (temperature), relative humidity (RH), surface pressure, windspeed, zonal and meridional wind speed components, and short-wave down-ward (SWD) radiation flux. The overall comparison revealed the best resultsfor surface pressure (0.98±0.02,R2mean±standard deviation [σR2]), followedby temperature (0.94±0.02), and SWD radiation flux (0.87±0.03) while windspeed (0.49±0.12), RH (0.42±0.20), zonal (0.163±0.15) and meridional windspeed (0.129±0.17) displayed poor results. We also found that certain variables(surface pressure, wind speed, meridional, and zonal wind speed) showed noseasonal dependency while others (temperature, RH, and SWD radiation flux)performed better during certain seasons. Improved results were observed whendecreasing the temporal resolution from one hour to one month for temper-ature, meridional and zonal wind speed, and SWD radiation flux. However,certain variables (RH and surface pressure) showed comparatively worse resultsfor monthly resolution. Overall, ERA5 performs well in the Arctic, but cautionneeds to be taken with wind speed and RH, which has implications for the useof ERA5 in global climate models. Our results are useful to the scientific com-munity as it assesses the confidence to be placed in each of the surface variablesproduced by ERA5.KEYWORDSArctic, ERA5, meteorology, reanalysis model/in-situ observation comparisonJakob Boyd Pernov and Jules Gros-Daillon contributed equally to this work.This is an open access article under the terms of theCreative Commons AttributionLicense, which permits use, distribution and reproduction in any medium, provided theoriginal work is properly cited.© 2024 The Authors.Quarterly Journal of the Royal Meteorological Societypublished by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society.Q J R Meteorol Soc. 2024;1–24.wileyonlinelibrary.com/journal/qj1