Clouds form when water vapor condenses into liquid water droplets or solid ice crystals. There are three main ways that air can be cooled enough for condensation to occur: contact cooling over land or sea surfaces, convection as air rises, and orographic lifting as air rises over mountains. Clouds can be classified based on their shape and height, with low-level clouds like stratus closest to the surface and high-level clouds like cirrus located over 6,000 meters. The major cloud belts around the world are associated with prevailing wind patterns.

1. Clouds John Harris - Head of Geography - Radley College - UK [email_address] http://geography.radley.org.uk

2. Water is strange stuff! Gas - water vapour (invisible) Liquid - water droplets (visible) Solid - ice crystals, hail, snow Water can occur in 3 states:

3. What are clouds? Clouds are formed of tiny droplets of water or ice. Clouds form when water vapour cools and condenses . The temperature at which condensation occurs is called dew point . Condensation also requires nucleii (small particles) such as dust.

4. What happens when air is cooled? Relative humidity increases. Dew point is reached (100% relative humidity). Water vapour (invisible) condenses to form water droplets (visible). Sometimes the water vapour may change straight into solid state: called sublimation .

5. How is air cooled? Contact eg with a cold surface such as over land in winter. Convection eg uplift over warm ground. Orographic eg rising over mountains. Frontal eg when a mass of warm air meets and rises over a mass of cold air.

6. Cloud shapes Clouds can be classified by their shape and height Flat clouds eg Stratus (St) Fluffy clouds eg Cumulus (Cu) Wispy clouds eg Cirrus (Ci)

7. Cloud heights Clouds can also be classified by height of cloudbase Low level (below 2000m) eg stratus Middle level - alto (2,000 to 6, 000m) eg alto-cumulus High level - cirro (above 6,000m) eg cirrus

8. Spot the cloud! Low and flat ….. Stratus

9. Spot the cloud! Middle level, fluffy ….. Alto -Cumulus

10. Spot the cloud! High level, wispy ….. Cirrus

11. Spot the cloud! Rain bearing, storm clouds ….. Cumulo-Nimbus

12. World cloud patterns Can you explain the major world cloud belts?