Near‐Surface Air Temperature Measurements: Contribution to the Overall Uncertainty due to Wind Speed and Relative Humidity

In the context of global warming, ensuring the comparability and traceability of air temperature measurements is essential for accurately characterising climate change. However, quantifying the environmental effects under real measurement conditions is still a key challenge for the meteorological community. This study addresses this issue by improving the understanding of air temperature observation uncertainties from ground-based stations. Data from six identical thermometers at 1.60 m and 2.10 m, protected with the same ventilated solar shield and connected to the same datalogger, were analysed during summer and winter. Air temperature difference (ΔT) was calculated as the difference between the readings of each thermometer and the mean, while wind speed and relative humidity were considered quantities of influence. The analysis shows that ΔT depends on season, sensor height, wind speed and relative humidity. During winter nights, ΔT reflects the influence of fog and condensation, intensified by low wind speed. ΔT also exhibits a clear diurnal cycle, indicating the presence of a solar heating effect. The uncertainty of ΔT was then calculated across different ranges of air temperature, wind speed, and relative humidity, obtaining values between 0.03°C and 0.12°C for both thermometer heights. For instance, during a summer daytime case, the air temperature at 1.60 m reached 32.25°C with an uncertainty due to wind speed and relative humidity equal to 0.06°C. Overall, the results show that the uncertainty decreases as wind speed increases, independently of seasonal conditions and thermometer height. This work provides uncertainty values derived from real environmental conditions that can be incorporated in the environmental effects component of the overall measurement uncertainty, in line with the World Meteorological Organisation requirements. These results also support the evaluation of uncertainty budgets for climate reference stations, providing uncertainty values applicable to other stations with similar measurement setups.