13. Measuring and Forecasting Weather Storage of Instruments
Some weather forecasting instruments, such as the barograph, the maximum and minimum thermometer and the hygrometer, are stored in a wooden box called a Stevenson screen.
6. Sunshine A Campbell−Stokes recorder measures the hours of sunshine in a day.
A solid glass ball concentrates the sun’s rays onto a removable strip of card, which is placed behind the ball.
The Stevenson screen is painted white to reflect the sun.
Gaps in the sides allow air but not direct sunlight to enter the box.
The Stevenson screen allows for more accurate measurements to be recorded.
The card is marked at hourly intervals.
As the sun shines through the ball, it scorches a mark on the paper.
A Campbell−Stokes recorder
Question Time
1. Name the three main types of clouds. 2. Which cloud type can bring heavy rain showers? 3. Choose one type of cloud and describe its appearance. 4. What unit of measurement is used to measure wind speed? 5. Explain how a wind vane or an anemometer works. 6. (a) What is relative humidity? (b) Which instrument is used to measure it?
7. (a) What does a Campbell−Stokes recorder measure? (b) How does it work?