GEOGRAPHY IGCSE: WEATHER MEASUREMENTS. It contains: difference between weather and climate, measuring the weather, what do we measure, temperature, precipitation, wind direction, Beaufort scale, cloud cover, air pressure, glossary.

1. IGCSE GEOGRAPHY
20. WEATHER & CLIMATE
WEATHER
MEASUREMENTS

2. Weather describes the day-to-day conditions of the
atmosphere. Weather can change quickly - one day it can be
dry and sunny and the next day it may rain.
Climate describes average weather conditions over longer
periods and over large areas.
The table shows the world climatic zones.

4. Weather affects us in many ways.
It affects what we do and what we wear, how we travel and even
our moods.
Meteorologists measure weather conditions in different places
and use this information to report and make forecasts about
future weather conditions.
This is useful because people can be warned about hazardous
weather conditions such as storms and floods.

5. Temperature
Precipitation, eg rainfall
Wind speed and direction
Cloud cover and visibility
Air pressure
Humidity (amount of water vapour in the air)
Sunshine

6. Temperature is measured in Celsius (°C) using a thermometer.
The thermometer must be shaded from direct sunlight and
should have air circulating around it.
The thermometers can be placed in a Stevenson Screen.
This is a wooden box with slatted sides, a sloping roof and
legs to keep the screen off the ground. It is painted white to
reflect the sun.

8. Precipitation is measured using a rain gauge.
This is a funnel inside a graduated container.
The depth of the rain in millimetres can be read from the side
of the container.

9. Wind direction is reported by the direction it is blowing from,
according to the compass.
Wind blowing from the west is travelling eastwards so is called a
westerly wind, not an easterly wind.
Wind speed can be measured using an anemometer.
The strength of the wind is measured on the Beaufort scale.

11. • Beaufort number 0 (Calm with wind speeds of almost zero)
• Beaufort number 1 (Drifting smoke with wind speeds around 1 to 3 kmph)
• Beaufort number 2 (Light breeze with wind speeds around 4 to 7 kmph)
• Beaufort number 3 (Gentle breeze with wind speeds at 8 to 12 kmph)
• Beaufort number 4 (Moderate. Wind speed between 13 and 17 kmph)
• Beaufort number 5 (Movement in trees. Wind speed up to 24 kmph)
• Beaufort number 6 (Strong breeze. Wind speed between 25 and 30 kmph)
• Beaufort number 7 (High wind. Wind speed between 31 and 38 kmph)
• Beaufort number 8 (Gale. Damage to trees. Wind speed up to 49 kmph)
• Beaufort number 9 (Strong gale. Wind speeds between 49 to 54 kmph)
• Beaufort number 10 (Storm. Wind speed between 55 and 63 kmph)
• Beaufort number 11 (Violent storm. Wind speeds between 64 and 73 kmph)
• Beaufort number 12 (Hurricane. Major damage. Wind speeds over 74 kmph)

12. Cloud cover is measured in units called oktas.
Each okta represents one eighth of the sky covered by cloud.

15. Air is light but because there is so much of it above us, it exerts a
pressure on us.
Air pressure is measured by a barometer. The units used are
millibars. The greater the reading, the higher the pressure.
A high-pressure system is called an anticyclone. Air falls in an
anticyclone so no clouds are formed. In summer, high pressure
usually results in clear skies, gentle breezes and fine weather. In
winter high pressure leads to clear skies and colder conditions.
An area of low pressure is called a depression. Air rises in a
depression so clouds and rainfall are formed. Depressions
therefore bring unsettled weather and rain. Winds are normally
stronger. They usually form over the Atlantic Ocean and are
carried across Britain by westerly winds.

17. Clouds are categorised according to height and shape.
The different categories of clouds are then given names based on
Latin words, eg nimbus clouds bring rain, stratus clouds appear
as layers.