Measuring air temperature on still nights

What is it about?

Air temperature measurement typically uses a slatted box - often called a Stevenson screen after the originator of a widely adopted design - to protect thermometers from rain and sunlight. To work well, there needs to be adequate wind to bring air across the thermometers. On calm summer nights, this requirement may not be met, and the temperatures obtained become less representative.

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Photo by Jarosław Kwoczała on Unsplash

Photo by Jarosław Kwoczała on Unsplash

Why is it important?

Night-time temperatures have a strong impact on human comfort. One measure adopted to monitor this is by counting how often a "Tropical Night" occurs, which is a night on which the minimum temperature does not fall below 20.0 Celsius. This article points out that the minimum temperature at night often coincides with calm conditions, making it a less than ideal time for an accurate temperature measurement using a Stevenson screen. One answer is to force-ventilate the thermometer, which has long been known to help but is still relatively little implemented.