Quantifying uncertainties in climate data: measurement limitations of naturally ventilated thermometer screens

Abstract Climate science depends on accurate air temperature measurement. To achieve this, well ventilated thermometers protected from direct sunlight and precipitation are needed, commonly through using louvred enclosures known as screens or shields. Maintaining good natural ventilation is critical for measurements. Ventilation effects uncertainties quantified here an aspirated thermometer a reference, temperatures spanning −2.8 °C to 35.5 °C. Of 81462 5 min mean values obtained, 50% were within ±0.07 of the reference only 2% lay beyond −0.66 0.47 °C, where negative represent naturally screen underestimating temperature. Larger absolute differences arose combination radiation exchange time response effects, which separated here. Firstly, 20s data, exponential shown vary with wind speed u −0.5 , exceeds conventional 1 averaging speeds up ms −1 (at 2 m height), increasing at least 15 when calm. Secondly, (both by day night) dominated low (<1 height). Insufficient damps recording extremes, potentially also influencing climatological means. A new method reduce presented. This reduces skew in bias −1.05 −0.26, and, almost 90% spread.