Abstract: | The performance of a Didcot-type thermometer screen on an Automatic Weather Station and a conventional Stevenson screen were compared, both with each other and against an aspirated Assmann psychrometer. Maximum temperature in the Didcot screen exceeded the conventional screen maximum by up to 1 K on calm, sunny days, and Didcot minimum temperatures were as much as 1.5 K less than the screen minima on still, clear nights; mean temperature discrepancies between screens were + 0.3 and − 0.4 K for maxima and minima, respectively. The apparent psychrometric constant for the Didcot screen was 1.0 mbar K−1 which increased to 1.2 mbar K−1 when u < 2 m s−1 in contrast to the value of 0.799 mbar K−1 frequently used for the Stevenson screen. |