Siting Weather Instruments

Last week we discovered what’s kept inside a Stevenson screen and I left you with a question.  So, why are only some of the weather station instruments kept inside the Stevenson screen?

Well think about what they are trying to measure. 

Perhaps you made your own rain gauge when we posted about it here.  You are certainly not going to catch much rain if the gauge is kept in a box.  For that matter you need to make sure it is well away from trees and other obstructions too or your measurement of rainfall won’t be accurate.

The sunshine recorder, wind vane and anemometer (to measure wind speed) also need to be out in the elements to make accurate measurements. 

The sunshine recorder needs to be on a site that is not shaded at any time of the day, so that if the sun is not behind clouds, the light is falling directly on the instrument. 

The wind vane and anemometer need to be up high so that they catch the full force of the wind, without it being deflected by buildings or trees or even funnelled by the shape of the ground.

So if the instruments need to be out in the weather to measure it accurately, how come the thermometers can do their job from inside the box?  We’ll find out next week.