Validation of atmospheric reanalyses over the central Arctic Ocean

Atmospheric reanalyses were validated against tethersonde sounding data on air temperature, air humidity and wind speed, collected during the drifting ice station Tara in the central Arctic in April–August 2007. The data were not assimilated into the reanalyses, providing a rare possibility for their independent validation, which was here made for the lowermost 890 m layer. The following reanalyses were included in the study: the European ERA‐Interim, the Japanese JCDAS, and the U.S. NCEP‐CFSR, NCEP‐DOE, and NASA‐MERRA. All reanalyses included large errors. ERA‐Interim was ranked first; it outperformed the other reanalyses in the bias and root‐mean‐square‐error (RMSE) for air temperature as well as in the bias, RMSE, and correlation coefficient for the wind speed. ERA‐Interim suffered, however, from a warm bias of up to 2°C in the lowermost 400 m layer and a moist bias of 0.3 to 0.5 g kg −1 throughout the 890 m layer. The NCEP‐CFSR, NCEP‐DOE, and NASA‐MERRA reanalyses outperformed the other reanalyses with respect to 2‐m air temperature and specific humidity and 10‐m wind speed, which makes them, especially NCEP‐CSFR, better in providing turbulent flux forcing for sea ice models. Considering the whole vertical profile, however, the older NCEP‐DOE got the second highest overall ranking, being better than the new NCEP‐CFSR. Considering the whole group of reanalyses, the largest air temperature errors surprisingly occurred during higher‐than‐average wind speeds. The observed biases in temperature, humidity, and wind speed were in many cases comparable or even larger than the climatological trends during the latest decades.