The Stevenson Screen is used to store all the thermometers and the hygrometer. It is essential that these instruments be shaded as the temperatures of the air (also called shade temperatures) are to be measured and not temperatures of the direct insolation.

Another reason for keeping these instruments in the Stevenson Screen to shelter them from precipitation.

Structure

The Stevenson Screen is a white wooden box. It is made of wood so that it does not conduct heat and painted white to reflect heat so as to not heat up the box.

The box is rested on stilts to lift it to a height of 1.2 m above the ground so as to reduce the effects of direct terrestrial radiation.

It also has other features to help keep out excessive heat so that the readings on the instruments are not affected by too much.

Firstly, it has a double-layered roof with intervening air space since air is a good insulator. Then, the box has louvred sides and a door to allow free air movement.

Siting of Stevenson Screen

It is placed in an open area, distanced from buildings, trees and walls to minimise their influence on the readings. Also, it is set up on short grass and not concrete, which heats up faster and thus affects the readings.

The box should be placed on level ground so that it is stable and the direction in which it faces is important too. The door should open away from direct sunlight to prevent direct sunlight from falling on the instruments.

Siting of other instruments

1. Rain gauge

The rain gauge should be placed on short grass in an open area where rain can enter it easily. It must be far away from buildings or any other obstructions to ensure accurate readings are taken.

The rain gauge is sunk into the ground with the rim 30 cm above ground to prevent splashing of water. Also, it should not be placed on concrete ground as rainwater may splash into it from the hard surface.

2. Anemometer and wind vane

They are erected well above the ground, away from obstructions such as tall trees and buildings to ensure accuracy of the readings. One good location is the top of the meteorological station.