These white louvered boxes can be found at every observing site. They protect the temperature sensors from being influenced by direct or reflected sunlight. Stevenson screens are always painted white to better reflect the sun's rays. The louvered sides allow outside air to flow around the thermometers. At some locations, the airflow is assisted by a psychrometer motor that pumps outside air across the instruments inside. You can see part of it sticking up above the screen--it looks a bit like a horn.
In the picture above, two hinges can be seen at the bottom of the door, with a latch at the top. The door swings down rather than to one side so that the wind won't catch it on windy days and rip it off the hinges. Stevenson screens are always installed so that the door opens facing north, to keep the sun from shining directly on the thermometers and affecting the readings.
If you'd like to learn about the different types of thermometers, visit our Thermometers section to see what goes on inside the Stevenson screen.
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