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How can we measure the weather?

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Which instruments are used to measure the weather?

How can you measure the weather?

Rainfall

Rain

is a type of

precipitation

. Precipitation is where water vapour in the air is cooled and condenses into water droplets. Other types of precipitation are snow, sleet, hail, dew or fog.

Rainfall is measured with a

rain gauge

3 of 28 rain gauge © Boardworks Ltd 2005

Temperature

Temperature

is how hot or cold it is.

How is temperature measured?

Temperature can be measured using a

thermometer

such as the liquid-in-glass type, where the liquid (mercury or spirit) in the bulb expands and rises up a capillary tube. Temperature is measured in either o Celsius or o Fahrenheit.

Temperatures are measured in the shade, so that the heat of the sun does not heat up the instrument being used.

4 of 28 Thermometer © Boardworks Ltd 2005

Wind

Wind

is simply moving air.

Wind speed

is how fast the air is moving.

How is wind speed measured?

Wind speed is measured by an

anemometer

. This has metal cups which rotate in the wind. The stronger the wind, the faster the anemometer turns.

5 of 28 anemometer © Boardworks Ltd 2005

Wind direction

How is

wind direction

measured?

Wind direction is measured using a

wind vane

In this case, the wind has come from the north. It is a

northerly

wind.

the arrow points into the wind 6 of 28 See if you can spot a wind vane in your local area.

Sunlight

Sunlight

is the amount of daylight.

How is sunlight measured?

The duration and the intensity of sunlight is measured using a

Campbell-Stokes sunshine recorder

. These focus light from the sun onto a piece of card where it leaves a burnt trace. The more sunshine there is, the longer the line. 7 of 28 © Boardworks Ltd 2005

Air pressure

Air pressure

is the force exerted on the Earth by the weight of the air above. How is air pressure measured?

It is measured with a

barometer

Weather instruments

Cloud cover

Cloud cover

is the fraction of the sky covered in clouds. Cloud cover can be measured by observation. It is measured in oktas.