8.8 Temperature and Heat Exchange Processes

8.8.2 Outline the measurement of surface air temperature in New Zealand (as reported in aviation observations), and relate that to actual temperatures experienced above a sealed or grass runway.

At an aerodrome, surface air temperature is measured using a thermometer housed in a Stevenson screen.

A Stevenson screen is designed to measure the temperature of the air, while reducing the effects of direct heating from the Sun and surrounding objects.

The screen is normally:

• painted matte white to reflect sunlight
• ventilated by slatted sides
• positioned so that direct sunlight does not shine on the thermometer
• mounted about 1.5 metres above the ground
• placed over a grassed surface, with grass surrounding the screen

This gives a standard temperature reading that can be compared between observing stations.

However, the actual temperature experienced by an aircraft near the surface may be different from the reported air temperature.